diff --git a/docs/README-migration.md b/docs/README-migration.md
index ae1693de7c..aa1b044f12 100644
--- a/docs/README-migration.md
+++ b/docs/README-migration.md
@@ -707,6 +707,8 @@ The following functions have been renamed:
 
 ## SDL_mutex.h
 
+SDL_LockMutex and SDL_UnlockMutex now return void; if the mutex is valid (including being a NULL pointer, which returns immediately), these functions never fail. If the mutex is invalid or the caller does something illegal, like unlock another thread's mutex, this is considered undefined behavior.
+
 The following functions have been renamed:
 * SDL_CondBroadcast() => SDL_BroadcastCondition()
 * SDL_CondSignal() => SDL_SignalCondition()
diff --git a/include/SDL3/SDL_mutex.h b/include/SDL3/SDL_mutex.h
index 23fb86c302..7dd150259f 100644
--- a/include/SDL3/SDL_mutex.h
+++ b/include/SDL3/SDL_mutex.h
@@ -169,13 +169,15 @@ extern DECLSPEC SDL_Mutex *SDLCALL SDL_CreateMutex(void);
  * unlock it the same number of times before it is actually made available for
  * other threads in the system (this is known as a "recursive mutex").
  *
+ * This function does not fail; if mutex is NULL, it will return immediately
+ * having locked nothing. If the mutex is valid, this function will always
+ * block until it can lock the mutex, and return with it locked.
+ *
  * \param mutex the mutex to lock
- * \returns 0 on success or a negative error code on failure; call
- *          SDL_GetError() for more information.
  *
  * \since This function is available since SDL 3.0.0.
  */
-extern DECLSPEC int SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
+extern DECLSPEC void SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
 
 /**
  * Try to lock a mutex without blocking.
@@ -186,9 +188,13 @@ extern DECLSPEC int SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
  * This technique is useful if you need exclusive access to a resource but
  * don't want to wait for it, and will return to it to try again later.
  *
+ * This function does not fail; if mutex is NULL, it will return 0 immediately
+ * having locked nothing. If the mutex is valid, this function will always
+ * either lock the mutex and return 0, or return SDL_MUTEX_TIMEOUT and lock
+ * nothing.
+ *
  * \param mutex the mutex to try to lock
- * \returns 0, `SDL_MUTEX_TIMEDOUT`, or -1 on error; call SDL_GetError() for
- *          more information.
+ * \returns 0 or `SDL_MUTEX_TIMEDOUT`
  *
  * \since This function is available since SDL 3.0.0.
  *
@@ -210,12 +216,10 @@ extern DECLSPEC int SDLCALL SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0
  * thread, and doing so results in undefined behavior.
  *
  * \param mutex the mutex to unlock.
- * \returns 0 on success or a negative error code on failure; call
- *          SDL_GetError() for more information.
  *
  * \since This function is available since SDL 3.0.0.
  */
-extern DECLSPEC int SDLCALL SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex);
+extern DECLSPEC void SDLCALL SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex);
 
 /**
  * Destroy a mutex created with SDL_CreateMutex().
@@ -321,15 +325,17 @@ extern DECLSPEC SDL_RWLock *SDLCALL SDL_CreateRWLock(void);
  * lock before requesting a read-only lock. (But, of course, if you have the
  * write lock, you don't need further locks to read in any case.)
  *
+ * This function does not fail; if rwlock is NULL, it will return immediately
+ * having locked nothing. If the rwlock is valid, this function will always
+ * block until it can lock the mutex, and return with it locked.
+ *
  * \param rwlock the read/write lock to lock
- * \returns 0 on success or a negative error code on failure; call
- *          SDL_GetError() for more information.
  *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_UnlockRWLock
  */
-extern DECLSPEC int SDLCALL SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock);
+extern DECLSPEC void SDLCALL SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock);
 
 /**
  * Lock the read/write lock for _write_ operations.
@@ -348,15 +354,17 @@ extern DECLSPEC int SDLCALL SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQ
  * read-only lock. Doing so results in undefined behavior. Unlock the
  * read-only lock before requesting a write lock.
  *
+ * This function does not fail; if rwlock is NULL, it will return immediately
+ * having locked nothing. If the rwlock is valid, this function will always
+ * block until it can lock the mutex, and return with it locked.
+ *
  * \param rwlock the read/write lock to lock
- * \returns 0 on success or a negative error code on failure; call
- *          SDL_GetError() for more information.
  *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_UnlockRWLock
  */
-extern DECLSPEC int SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock);
+extern DECLSPEC void SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock);
 
 /**
  * Try to lock a read/write lock _for reading_ without blocking.
@@ -370,9 +378,13 @@ extern DECLSPEC int SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQ
  * Trying to lock for read-only access can succeed if other threads are
  * holding read-only locks, as this won't prevent access.
  *
+ * This function does not fail; if rwlock is NULL, it will return 0 immediately
+ * having locked nothing. If rwlock is valid, this function will always
+ * either lock the rwlock and return 0, or return SDL_RWLOCK_TIMEOUT and lock
+ * nothing.
+ *
  * \param rwlock the rwlock to try to lock
- * \returns 0, `SDL_RWLOCK_TIMEDOUT`, or -1 on error; call SDL_GetError() for
- *          more information.
+ * \returns 0 or `SDL_RWLOCK_TIMEDOUT`
  *
  * \since This function is available since SDL 3.0.0.
  *
@@ -400,9 +412,13 @@ extern DECLSPEC int SDLCALL SDL_TryLockRWLockForReading(SDL_RWLock *rwlock) SDL_
  * read-only lock. Doing so results in undefined behavior. Unlock the
  * read-only lock before requesting a write lock.
  *
+ * This function does not fail; if rwlock is NULL, it will return 0 immediately
+ * having locked nothing. If rwlock is valid, this function will always
+ * either lock the rwlock and return 0, or return SDL_RWLOCK_TIMEOUT and lock
+ * nothing.
+ *
  * \param rwlock the rwlock to try to lock
- * \returns 0, `SDL_RWLOCK_TIMEDOUT`, or -1 on error; call SDL_GetError() for
- *          more information.
+ * \returns 0 or `SDL_RWLOCK_TIMEDOUT`
  *
  * \since This function is available since SDL 3.0.0.
  *
@@ -428,12 +444,10 @@ extern DECLSPEC int SDLCALL SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_
  * thread, and doing so results in undefined behavior.
  *
  * \param rwlock the rwlock to unlock.
- * \returns 0 on success or a negative error code on failure; call
- *          SDL_GetError() for more information.
  *
  * \since This function is available since SDL 3.0.0.
  */
-extern DECLSPEC int SDLCALL SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock);
+extern DECLSPEC void SDLCALL SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock);
 
 /**
  * Destroy a read/write lock created with SDL_CreateRWLock().
diff --git a/src/SDL_properties.c b/src/SDL_properties.c
index 22613752d3..0b8d795347 100644
--- a/src/SDL_properties.c
+++ b/src/SDL_properties.c
@@ -123,17 +123,16 @@ SDL_PropertiesID SDL_CreateProperties(void)
         goto error;
     }
 
-    if (SDL_LockRWLockForWriting(SDL_properties_lock) == 0) {
+    SDL_LockRWLockForWriting(SDL_properties_lock);
+    ++SDL_last_properties_id;
+    if (SDL_last_properties_id == 0) {
         ++SDL_last_properties_id;
-        if (SDL_last_properties_id == 0) {
-            ++SDL_last_properties_id;
-        }
-        props = SDL_last_properties_id;
-        if (SDL_InsertIntoHashTable(SDL_properties, (const void *)(uintptr_t)props, properties)) {
-            inserted = SDL_TRUE;
-        }
-        SDL_UnlockRWLock(SDL_properties_lock);
     }
+    props = SDL_last_properties_id;
+    if (SDL_InsertIntoHashTable(SDL_properties, (const void *)(uintptr_t)props, properties)) {
+        inserted = SDL_TRUE;
+    }
+    SDL_UnlockRWLock(SDL_properties_lock);
 
     if (inserted) {
         /* All done! */
@@ -152,15 +151,17 @@ int SDL_LockProperties(SDL_PropertiesID props)
     if (!props) {
         return SDL_InvalidParamError("props");
     }
-    if (SDL_LockRWLockForReading(SDL_properties_lock) == 0) {
-        SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
-        SDL_UnlockRWLock(SDL_properties_lock);
-    }
+
+    SDL_LockRWLockForReading(SDL_properties_lock);
+    SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
+    SDL_UnlockRWLock(SDL_properties_lock);
+
     if (!properties) {
-        SDL_InvalidParamError("props");
-        return -1;
+        return SDL_InvalidParamError("props");
     }
-    return SDL_LockMutex(properties->lock);
+
+    SDL_LockMutex(properties->lock);
+    return 0;
 }
 
 void SDL_UnlockProperties(SDL_PropertiesID props)
@@ -170,13 +171,15 @@ void SDL_UnlockProperties(SDL_PropertiesID props)
     if (!props) {
         return;
     }
-    if (SDL_LockRWLockForReading(SDL_properties_lock) == 0) {
-        SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
-        SDL_UnlockRWLock(SDL_properties_lock);
-    }
+
+    SDL_LockRWLockForReading(SDL_properties_lock);
+    SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
+    SDL_UnlockRWLock(SDL_properties_lock);
+
     if (!properties) {
         return;
     }
+
     SDL_UnlockMutex(properties->lock);
 }
 
@@ -193,10 +196,10 @@ int SDL_SetProperty(SDL_PropertiesID props, const char *name, void *value, void
         return SDL_InvalidParamError("name");
     }
 
-    if (SDL_LockRWLockForReading(SDL_properties_lock) == 0) {
-        SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
-        SDL_UnlockRWLock(SDL_properties_lock);
-    }
+    SDL_LockRWLockForReading(SDL_properties_lock);
+    SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
+    SDL_UnlockRWLock(SDL_properties_lock);
+
     if (!properties) {
         return SDL_InvalidParamError("props");
     }
@@ -242,10 +245,10 @@ void *SDL_GetProperty(SDL_PropertiesID props, const char *name)
         return NULL;
     }
 
-    if (SDL_LockRWLockForReading(SDL_properties_lock) == 0) {
-        SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
-        SDL_UnlockRWLock(SDL_properties_lock);
-    }
+    SDL_LockRWLockForReading(SDL_properties_lock);
+    SDL_FindInHashTable(SDL_properties, (const void *)(uintptr_t)props, (const void **)&properties);
+    SDL_UnlockRWLock(SDL_properties_lock);
+
     if (!properties) {
         SDL_InvalidParamError("props");
         return NULL;
@@ -280,8 +283,7 @@ void SDL_DestroyProperties(SDL_PropertiesID props)
         return;
     }
 
-    if (SDL_LockRWLockForWriting(SDL_properties_lock) == 0) {
-        SDL_RemoveFromHashTable(SDL_properties, (const void *)(uintptr_t)props);
-        SDL_UnlockRWLock(SDL_properties_lock);
-    }
+    SDL_LockRWLockForWriting(SDL_properties_lock);
+    SDL_RemoveFromHashTable(SDL_properties, (const void *)(uintptr_t)props);
+    SDL_UnlockRWLock(SDL_properties_lock);
 }
diff --git a/src/audio/SDL_audiocvt.c b/src/audio/SDL_audiocvt.c
index 7681e76cb9..b64ca480dc 100644
--- a/src/audio/SDL_audiocvt.c
+++ b/src/audio/SDL_audiocvt.c
@@ -476,12 +476,20 @@ int SDL_SetAudioStreamPutCallback(SDL_AudioStream *stream, SDL_AudioStreamCallba
 
 int SDL_LockAudioStream(SDL_AudioStream *stream)
 {
-    return stream ? SDL_LockMutex(stream->lock) : SDL_InvalidParamError("stream");
+    if (!stream) {
+        return SDL_InvalidParamError("stream");
+    }
+    SDL_LockMutex(stream->lock);
+    return 0;
 }
 
 int SDL_UnlockAudioStream(SDL_AudioStream *stream)
 {
-    return stream ? SDL_UnlockMutex(stream->lock) : SDL_InvalidParamError("stream");
+    if (!stream) {
+        return SDL_InvalidParamError("stream");
+    }
+    SDL_UnlockMutex(stream->lock);
+    return 0;
 }
 
 int SDL_GetAudioStreamFormat(SDL_AudioStream *stream, SDL_AudioSpec *src_spec, SDL_AudioSpec *dst_spec)
diff --git a/src/dynapi/SDL_dynapi_procs.h b/src/dynapi/SDL_dynapi_procs.h
index b8ac62c583..ac41615e9d 100644
--- a/src/dynapi/SDL_dynapi_procs.h
+++ b/src/dynapi/SDL_dynapi_procs.h
@@ -519,9 +519,9 @@ SDL_DYNAPI_PROC(void*,SDL_LoadFile_RW,(SDL_RWops *a, size_t *b, SDL_bool c),(a,b
 SDL_DYNAPI_PROC(SDL_FunctionPointer,SDL_LoadFunction,(void *a, const char *b),(a,b),return)
 SDL_DYNAPI_PROC(void*,SDL_LoadObject,(const char *a),(a),return)
 SDL_DYNAPI_PROC(void,SDL_LockJoysticks,(void),(),)
-SDL_DYNAPI_PROC(int,SDL_LockMutex,(SDL_Mutex *a),(a),return)
-SDL_DYNAPI_PROC(int,SDL_LockRWLockForReading,(SDL_RWLock *a),(a),return)
-SDL_DYNAPI_PROC(int,SDL_LockRWLockForWriting,(SDL_RWLock *a),(a),return)
+SDL_DYNAPI_PROC(void,SDL_LockMutex,(SDL_Mutex *a),(a),)
+SDL_DYNAPI_PROC(void,SDL_LockRWLockForReading,(SDL_RWLock *a),(a),)
+SDL_DYNAPI_PROC(void,SDL_LockRWLockForWriting,(SDL_RWLock *a),(a),)
 SDL_DYNAPI_PROC(int,SDL_LockSurface,(SDL_Surface *a),(a),return)
 SDL_DYNAPI_PROC(int,SDL_LockTexture,(SDL_Texture *a, const SDL_Rect *b, void **c, int *d),(a,b,c,d),return)
 SDL_DYNAPI_PROC(int,SDL_LockTextureToSurface,(SDL_Texture *a, const SDL_Rect *b, SDL_Surface **c),(a,b,c),return)
@@ -706,8 +706,8 @@ SDL_DYNAPI_PROC(int,SDL_TryLockRWLockForWriting,(SDL_RWLock *a),(a),return)
 SDL_DYNAPI_PROC(int,SDL_TryWaitSemaphore,(SDL_Semaphore *a),(a),return)
 SDL_DYNAPI_PROC(void,SDL_UnloadObject,(void *a),(a),)
 SDL_DYNAPI_PROC(void,SDL_UnlockJoysticks,(void),(),)
-SDL_DYNAPI_PROC(int,SDL_UnlockMutex,(SDL_Mutex *a),(a),return)
-SDL_DYNAPI_PROC(int,SDL_UnlockRWLock,(SDL_RWLock *a),(a),return)
+SDL_DYNAPI_PROC(void,SDL_UnlockMutex,(SDL_Mutex *a),(a),)
+SDL_DYNAPI_PROC(void,SDL_UnlockRWLock,(SDL_RWLock *a),(a),)
 SDL_DYNAPI_PROC(void,SDL_UnlockSurface,(SDL_Surface *a),(a),)
 SDL_DYNAPI_PROC(void,SDL_UnlockTexture,(SDL_Texture *a),(a),)
 SDL_DYNAPI_PROC(void,SDL_UpdateGamepads,(void),(),)
diff --git a/src/thread/generic/SDL_sysmutex.c b/src/thread/generic/SDL_sysmutex.c
index 8d4a3702d1..579d028ee3 100644
--- a/src/thread/generic/SDL_sysmutex.c
+++ b/src/thread/generic/SDL_sysmutex.c
@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-/* An implementation of mutexes using semaphores */
+// An implementation of mutexes using semaphores
 
 #include "SDL_systhread_c.h"
 
@@ -31,13 +31,9 @@ struct SDL_Mutex
     SDL_Semaphore *sem;
 };
 
-/* Create a mutex */
 SDL_Mutex *SDL_CreateMutex(void)
 {
-    SDL_Mutex *mutex;
-
-    /* Allocate mutex memory */
-    mutex = (SDL_Mutex *)SDL_calloc(1, sizeof(*mutex));
+    SDL_Mutex *mutex = (SDL_Mutex *)SDL_calloc(1, sizeof(*mutex));
 
 #ifndef SDL_THREADS_DISABLED
     if (mutex) {
@@ -52,12 +48,11 @@ SDL_Mutex *SDL_CreateMutex(void)
     } else {
         SDL_OutOfMemory();
     }
-#endif /* !SDL_THREADS_DISABLED */
+#endif // !SDL_THREADS_DISABLED
 
     return mutex;
 }
 
-/* Free the mutex */
 void SDL_DestroyMutex(SDL_Mutex *mutex)
 {
     if (mutex) {
@@ -68,94 +63,72 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
     }
 }
 
-/* Lock the mutex */
-int SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    SDL_threadID this_thread;
-
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    this_thread = SDL_ThreadID();
-    if (mutex->owner == this_thread) {
-        ++mutex->recursive;
-    } else {
-        /* The order of operations is important.
-           We set the locking thread id after we obtain the lock
-           so unlocks from other threads will fail.
-         */
-        SDL_WaitSemaphore(mutex->sem);
-        mutex->owner = this_thread;
-        mutex->recursive = 0;
-    }
-
-    return 0;
-#endif /* SDL_THREADS_DISABLED */
-}
-
-/* try Lock the mutex */
-int SDL_TryLockMutex(SDL_Mutex *mutex)
-{
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    int retval = 0;
-    SDL_threadID this_thread;
-
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    this_thread = SDL_ThreadID();
-    if (mutex->owner == this_thread) {
-        ++mutex->recursive;
-    } else {
-        /* The order of operations is important.
-         We set the locking thread id after we obtain the lock
-         so unlocks from other threads will fail.
-         */
-        retval = SDL_TryWaitSemaphore(mutex->sem);
-        if (retval == 0) {
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        SDL_threadID this_thread = SDL_ThreadID();
+        if (mutex->owner == this_thread) {
+            ++mutex->recursive;
+        } else {
+            /* The order of operations is important.
+               We set the locking thread id after we obtain the lock
+               so unlocks from other threads will fail.
+             */
+            SDL_WaitSemaphore(mutex->sem);
             mutex->owner = this_thread;
             mutex->recursive = 0;
         }
     }
-
-    return retval;
 #endif /* SDL_THREADS_DISABLED */
 }
 
-/* Unlock the mutex */
-int SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    if (mutex == NULL) {
-        return 0;
+    int retval = 0;
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        SDL_threadID this_thread = SDL_ThreadID();
+        if (mutex->owner == this_thread) {
+            ++mutex->recursive;
+        } else {
+            /* The order of operations is important.
+             We set the locking thread id after we obtain the lock
+             so unlocks from other threads will fail.
+             */
+            retval = SDL_TryWaitSemaphore(mutex->sem);
+            if (retval == 0) {
+                mutex->owner = this_thread;
+                mutex->recursive = 0;
+            }
+        }
     }
-
-    /* If we don't own the mutex, we can't unlock it */
-    if (SDL_ThreadID() != mutex->owner) {
-        return SDL_SetError("mutex not owned by this thread");
-    }
-
-    if (mutex->recursive) {
-        --mutex->recursive;
-    } else {
-        /* The order of operations is important.
-           First reset the owner so another thread doesn't lock
-           the mutex and set the ownership before we reset it,
-           then release the lock semaphore.
-         */
-        mutex->owner = 0;
-        SDL_PostSemaphore(mutex->sem);
-    }
-    return 0;
-#endif /* SDL_THREADS_DISABLED */
+#endif // SDL_THREADS_DISABLED
+    return retval;
+}
+
+void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
+{
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        // If we don't own the mutex, we can't unlock it
+        if (SDL_ThreadID() != mutex->owner) {
+            SDL_assert(!"Tried to unlock a mutex we don't own!");
+            return; // (undefined behavior!) SDL_SetError("mutex not owned by this thread");
+        }
+
+        if (mutex->recursive) {
+            --mutex->recursive;
+        } else {
+            /* The order of operations is important.
+               First reset the owner so another thread doesn't lock
+               the mutex and set the ownership before we reset it,
+               then release the lock semaphore.
+             */
+            mutex->owner = 0;
+            SDL_PostSemaphore(mutex->sem);
+        }
+    }
+#endif // SDL_THREADS_DISABLED
 }
 
diff --git a/src/thread/generic/SDL_sysrwlock.c b/src/thread/generic/SDL_sysrwlock.c
index d88bee15d3..a38b81d6ac 100644
--- a/src/thread/generic/SDL_sysrwlock.c
+++ b/src/thread/generic/SDL_sysrwlock.c
@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-/* An implementation of rwlocks using mutexes, condition variables, and atomics. */
+// An implementation of rwlocks using mutexes, condition variables, and atomics.
 
 #include "SDL_systhread_c.h"
 
@@ -30,7 +30,7 @@
  * will be chosen at runtime), the function names need to be
  * suffixed
  */
-/* !!! FIXME: this is quite a tapdance with macros and the build system, maybe we can simplify how we do this. --ryan. */
+// !!! FIXME: this is quite a tapdance with macros and the build system, maybe we can simplify how we do this. --ryan.
 #ifndef SDL_THREAD_GENERIC_RWLOCK_SUFFIX
 #define SDL_CreateRWLock_generic SDL_CreateRWLock
 #define SDL_DestroyRWLock_generic SDL_DestroyRWLock
@@ -95,63 +95,48 @@ void SDL_DestroyRWLock_generic(SDL_RWLock *rwlock)
     }
 }
 
-int SDL_LockRWLockForReading_generic(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockRWLockForReading_generic(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
 #ifndef SDL_THREADS_DISABLED
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (SDL_LockMutex(rwlock->lock) == -1) {
-        return -1;
+    if (rwlock) {
+        // !!! FIXME: these don't have to be atomic, we always gate them behind a mutex.
+        SDL_LockMutex(rwlock->lock);
+        SDL_assert(SDL_AtomicGet(&rwlock->writer_count) == 0);  // shouldn't be able to grab lock if there's a writer!
+        SDL_AtomicAdd(&rwlock->reader_count, 1);
+        SDL_UnlockMutex(rwlock->lock);   // other readers can attempt to share the lock.
     }
-
-    SDL_assert(SDL_AtomicGet(&rwlock->writer_count) == 0);  /* shouldn't be able to grab lock if there's a writer! */
-
-    SDL_AtomicAdd(&rwlock->reader_count, 1);
-    SDL_UnlockMutex(rwlock->lock);   /* other readers can attempt to share the lock. */
 #endif
-
-    return 0;
 }
 
-int SDL_LockRWLockForWriting_generic(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockRWLockForWriting_generic(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
 #ifndef SDL_THREADS_DISABLED
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (SDL_LockMutex(rwlock->lock) == -1) {
-        return -1;
-    }
+    if (rwlock) {
+        SDL_LockMutex(rwlock->lock);
+        while (SDL_AtomicGet(&rwlock->reader_count) > 0) {  // while something is holding the shared lock, keep waiting.
+            SDL_WaitCondition(rwlock->condition, rwlock->lock);  // release the lock and wait for readers holding the shared lock to release it, regrab the lock.
+        }
 
-    while (SDL_AtomicGet(&rwlock->reader_count) > 0) {  /* while something is holding the shared lock, keep waiting. */
-        SDL_WaitCondition(rwlock->condition, rwlock->lock);  /* release the lock and wait for readers holding the shared lock to release it, regrab the lock. */
+        // we hold the lock!
+        SDL_AtomicAdd(&rwlock->writer_count, 1);  // we let these be recursive, but the API doesn't require this. It _does_ trust you unlock correctly!
     }
-
-    /* we hold the lock! */
-    SDL_AtomicAdd(&rwlock->writer_count, 1);  /* we let these be recursive, but the API doesn't require this. It _does_ trust you unlock correctly! */
 #endif
-
-    return 0;
 }
 
 int SDL_TryLockRWLockForReading_generic(SDL_RWLock *rwlock)
 {
 #ifndef SDL_THREADS_DISABLED
-    int rc;
+    if (rwlock) {
+        const int rc = SDL_TryLockMutex(rwlock->lock);
+        if (rc != 0) {
+            // !!! FIXME: there is a small window where a reader has to lock the mutex, and if we hit that, we will return SDL_RWLOCK_TIMEDOUT even though we could have shared the lock.
+            return rc;
+        }
 
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
+        SDL_assert(SDL_AtomicGet(&rwlock->writer_count) == 0);  // shouldn't be able to grab lock if there's a writer!
+        SDL_AtomicAdd(&rwlock->reader_count, 1);
+        SDL_UnlockMutex(rwlock->lock);   // other readers can attempt to share the lock.
     }
-
-    rc = SDL_TryLockMutex(rwlock->lock);
-    if (rc != 0) {
-        /* !!! FIXME: there is a small window where a reader has to lock the mutex, and if we hit that, we will return SDL_RWLOCK_TIMEDOUT even though we could have shared the lock. */
-        return rc;
-    }
-
-    SDL_assert(SDL_AtomicGet(&rwlock->writer_count) == 0);  /* shouldn't be able to grab lock if there's a writer! */
-
-    SDL_AtomicAdd(&rwlock->reader_count, 1);
-    SDL_UnlockMutex(rwlock->lock);   /* other readers can attempt to share the lock. */
 #endif
 
     return 0;
@@ -160,46 +145,41 @@ int SDL_TryLockRWLockForReading_generic(SDL_RWLock *rwlock)
 int SDL_TryLockRWLockForWriting_generic(SDL_RWLock *rwlock)
 {
 #ifndef SDL_THREADS_DISABLED
-    int rc;
+    if (rwlock) {
+        const int rc = SDL_TryLockMutex(rwlock->lock);
+        if (rc != 0) {
+            return rc;
+        }
 
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
-    } else if ((rc = SDL_TryLockMutex(rwlock->lock)) != 0) {
-        return rc;
+        if (SDL_AtomicGet(&rwlock->reader_count) > 0) {  // a reader is using the shared lock, treat it as unavailable.
+            SDL_UnlockMutex(rwlock->lock);
+            return SDL_RWLOCK_TIMEDOUT;
+        }
+
+        // we hold the lock!
+        SDL_AtomicAdd(&rwlock->writer_count, 1);  // we let these be recursive, but the API doesn't require this. It _does_ trust you unlock correctly!
     }
-
-    if (SDL_AtomicGet(&rwlock->reader_count) > 0) {  /* a reader is using the shared lock, treat it as unavailable. */
-        SDL_UnlockMutex(rwlock->lock);
-        return SDL_RWLOCK_TIMEDOUT;
-    }
-
-    /* we hold the lock! */
-    SDL_AtomicAdd(&rwlock->writer_count, 1);  /* we let these be recursive, but the API doesn't require this. It _does_ trust you unlock correctly! */
 #endif
 
     return 0;
 }
 
-int SDL_UnlockRWLock_generic(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockRWLock_generic(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
 #ifndef SDL_THREADS_DISABLED
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
+    if (rwlock) {
+        SDL_LockMutex(rwlock->lock);  // recursive lock for writers, readers grab lock to make sure things are sane.
+
+        if (SDL_AtomicGet(&rwlock->reader_count) > 0) {  // we're a reader
+            SDL_AtomicAdd(&rwlock->reader_count, -1);
+            SDL_BroadcastCondition(rwlock->condition);  // alert any pending writers to attempt to try to grab the lock again.
+        } else if (SDL_AtomicGet(&rwlock->writer_count) > 0) {  // we're a writer
+            SDL_AtomicAdd(&rwlock->writer_count, -1);
+            SDL_UnlockMutex(rwlock->lock);  // recursive unlock.
+        }
+
+        SDL_UnlockMutex(rwlock->lock);
     }
-
-    SDL_LockMutex(rwlock->lock);  /* recursive lock for writers, readers grab lock to make sure things are sane. */
-
-    if (SDL_AtomicGet(&rwlock->reader_count) > 0) {  /* we're a reader */
-        SDL_AtomicAdd(&rwlock->reader_count, -1);
-        SDL_BroadcastCondition(rwlock->condition);  /* alert any pending writers to attempt to try to grab the lock again. */
-    } else if (SDL_AtomicGet(&rwlock->writer_count) > 0) {  /* we're a writer */
-        SDL_AtomicAdd(&rwlock->writer_count, -1);
-        SDL_UnlockMutex(rwlock->lock);  /* recursive unlock. */
-    }
-
-    SDL_UnlockMutex(rwlock->lock);
 #endif
-
-    return 0;
 }
 
diff --git a/src/thread/generic/SDL_sysrwlock_c.h b/src/thread/generic/SDL_sysrwlock_c.h
index 8247f8ebe6..9083cc89c8 100644
--- a/src/thread/generic/SDL_sysrwlock_c.h
+++ b/src/thread/generic/SDL_sysrwlock_c.h
@@ -27,12 +27,12 @@
 
 SDL_RWLock *SDL_CreateRWLock_generic(void);
 void SDL_DestroyRWLock_generic(SDL_RWLock *rwlock);
-int SDL_LockRWLockForReading_generic(SDL_RWLock *rwlock);
-int SDL_LockRWLockForWriting_generic(SDL_RWLock *rwlock);
+void SDL_LockRWLockForReading_generic(SDL_RWLock *rwlock);
+void  SDL_LockRWLockForWriting_generic(SDL_RWLock *rwlock);
 int SDL_TryLockRWLockForReading_generic(SDL_RWLock *rwlock);
 int SDL_TryLockRWLockForWriting_generic(SDL_RWLock *rwlock);
-int SDL_UnlockRWLock_generic(SDL_RWLock *rwlock);
+void SDL_UnlockRWLock_generic(SDL_RWLock *rwlock);
 
-#endif /* SDL_THREAD_GENERIC_RWLOCK_SUFFIX */
+#endif // SDL_THREAD_GENERIC_RWLOCK_SUFFIX
 
-#endif /* SDL_sysrwlock_c_h_ */
+#endif // SDL_sysrwlock_c_h_
diff --git a/src/thread/n3ds/SDL_sysmutex.c b/src/thread/n3ds/SDL_sysmutex.c
index 0995ad11f4..47e848582d 100644
--- a/src/thread/n3ds/SDL_sysmutex.c
+++ b/src/thread/n3ds/SDL_sysmutex.c
@@ -22,17 +22,13 @@
 
 #ifdef SDL_THREAD_N3DS
 
-/* An implementation of mutexes using libctru's RecursiveLock */
+// An implementation of mutexes using libctru's RecursiveLock
 
 #include "SDL_sysmutex_c.h"
 
-/* Create a mutex */
 SDL_Mutex *SDL_CreateMutex(void)
 {
-    SDL_Mutex *mutex;
-
-    /* Allocate mutex memory */
-    mutex = (SDL_Mutex *)SDL_malloc(sizeof(*mutex));
+    SDL_Mutex *mutex = (SDL_Mutex *)SDL_malloc(sizeof(*mutex));
     if (mutex) {
         RecursiveLock_Init(&mutex->lock);
     } else {
@@ -41,7 +37,6 @@ SDL_Mutex *SDL_CreateMutex(void)
     return mutex;
 }
 
-/* Free the mutex */
 void SDL_DestroyMutex(SDL_Mutex *mutex)
 {
     if (mutex) {
@@ -49,38 +44,23 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
     }
 }
 
-/* Lock the mutex */
-int SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        RecursiveLock_Lock(&mutex->lock);
     }
-
-    RecursiveLock_Lock(&mutex->lock);
-
-    return 0;
 }
 
-/* try Lock the mutex */
 int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    return RecursiveLock_TryLock(&mutex->lock);
+    return (mutex == NULL) ? 0 : RecursiveLock_TryLock(&mutex->lock);
 }
 
-/* Unlock the mutex */
-int SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS // clang doesn't know about NULL mutexes
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        RecursiveLock_Unlock(&mutex->lock);
     }
-
-    RecursiveLock_Unlock(&mutex->lock);
-
-    return 0;
 }
 
-#endif /* SDL_THREAD_N3DS */
+#endif // SDL_THREAD_N3DS
diff --git a/src/thread/ngage/SDL_sysmutex.cpp b/src/thread/ngage/SDL_sysmutex.cpp
index 9cc47d424d..4d5e3b08cd 100644
--- a/src/thread/ngage/SDL_sysmutex.cpp
+++ b/src/thread/ngage/SDL_sysmutex.cpp
@@ -67,17 +67,13 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
 }
 
 /* Lock the mutex */
-int SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        RMutex rmutex;
+        rmutex.SetHandle(mutex->handle);
+        rmutex.Wait();
     }
-
-    RMutex rmutex;
-    rmutex.SetHandle(mutex->handle);
-    rmutex.Wait();
-
-    return 0;
 }
 
 /* Try to lock the mutex */
@@ -95,16 +91,12 @@ int SDL_TryLockMutex(SDL_Mutex *mutex)
 #endif
 
 /* Unlock the mutex */
-int SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        RMutex rmutex;
+        rmutex.SetHandle(mutex->handle);
+        rmutex.Signal();
     }
-
-    RMutex rmutex;
-    rmutex.SetHandle(mutex->handle);
-    rmutex.Signal();
-
-    return 0;
 }
 
diff --git a/src/thread/psp/SDL_sysmutex.c b/src/thread/psp/SDL_sysmutex.c
index 8aaa96224d..f6701bb123 100644
--- a/src/thread/psp/SDL_sysmutex.c
+++ b/src/thread/psp/SDL_sysmutex.c
@@ -22,7 +22,7 @@
 
 #ifdef SDL_THREAD_PSP
 
-/* An implementation of mutexes using semaphores */
+// An implementation of mutexes using semaphores
 
 #include "SDL_systhread_c.h"
 
@@ -36,17 +36,11 @@ struct SDL_Mutex
     SceLwMutexWorkarea lock;
 };
 
-/* Create a mutex */
 SDL_Mutex *SDL_CreateMutex(void)
 {
-    SDL_Mutex *mutex = NULL;
-    SceInt32 res = 0;
-
-    /* Allocate mutex memory */
-    mutex = (SDL_Mutex *)SDL_malloc(sizeof(*mutex));
+    SDL_Mutex *mutex = (SDL_Mutex *)SDL_malloc(sizeof(*mutex));
     if (mutex) {
-
-        res = sceKernelCreateLwMutex(
+        const SceInt32 res = sceKernelCreateLwMutex(
             &mutex->lock,
             "SDL mutex",
             SCE_KERNEL_MUTEX_ATTR_RECURSIVE,
@@ -54,6 +48,8 @@ SDL_Mutex *SDL_CreateMutex(void)
             NULL);
 
         if (res < 0) {
+            SDL_free(mutex);
+            mutex = NULL;
             SDL_SetError("Error trying to create mutex: %lx", res);
         }
     } else {
@@ -62,7 +58,6 @@ SDL_Mutex *SDL_CreateMutex(void)
     return mutex;
 }
 
-/* Free the mutex */
 void SDL_DestroyMutex(SDL_Mutex *mutex)
 {
     if (mutex) {
@@ -71,75 +66,43 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
     }
 }
 
-/* Lock the mutex */
-int SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    SceInt32 res = 0;
-
-    if (mutex == NULL) {
-        return 0;
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        const SceInt32 res = sceKernelLockLwMutex(&mutex->lock, 1, NULL);
+        SDL_assert(res == SCE_KERNEL_ERROR_OK);  // assume we're in a lot of trouble if this assert fails.
     }
-
-    res = sceKernelLockLwMutex(&mutex->lock, 1, NULL);
-    if (res != SCE_KERNEL_ERROR_OK) {
-        return SDL_SetError("Error trying to lock mutex: %lx", res);
-    }
-
-    return 0;
-#endif /* SDL_THREADS_DISABLED */
+#endif // SDL_THREADS_DISABLED
 }
 
-/* Try to lock the mutex */
 int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    SceInt32 res = 0;
-
-    if (mutex == NULL) {
-        return 0;
+    int retval = 0;
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        const SceInt32 res = sceKernelTryLockLwMutex(&mutex->lock, 1);
+        if (res == SCE_KERNEL_ERROR_OK) {
+            retval = 0;
+        } else if (res == SCE_KERNEL_ERROR_WAIT_TIMEOUT) {
+            retval = SDL_MUTEX_TIMEDOUT;
+        } else {
+            SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
+            retval = SDL_MUTEX_TIMEDOUT;
+        }
     }
-
-    res = sceKernelTryLockLwMutex(&mutex->lock, 1);
-    switch (res) {
-    case SCE_KERNEL_ERROR_OK:
-        return 0;
-        break;
-    case SCE_KERNEL_ERROR_WAIT_TIMEOUT:
-        return SDL_MUTEX_TIMEDOUT;
-        break;
-    default:
-        return SDL_SetError("Error trying to lock mutex: %lx", res);
-        break;
-    }
-
-    return -1;
-#endif /* SDL_THREADS_DISABLED */
+#endif // SDL_THREADS_DISABLED
+    return retval;
 }
 
-/* Unlock the mutex */
-int SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    SceInt32 res = 0;
-
-    if (mutex == NULL) {
-        return 0;
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        const SceInt32 res = sceKernelUnlockLwMutex(&mutex->lock, 1);
+        SDL_assert(res == 0);  // assume we're in a lot of trouble if this assert fails.
     }
-
-    res = sceKernelUnlockLwMutex(&mutex->lock, 1);
-    if (res != 0) {
-        return SDL_SetError("Error trying to unlock mutex: %lx", res);
-    }
-
-    return 0;
-#endif /* SDL_THREADS_DISABLED */
+#endif // SDL_THREADS_DISABLED
 }
 
-#endif /* SDL_THREAD_PSP */
+#endif // SDL_THREAD_PSP
diff --git a/src/thread/pthread/SDL_sysmutex.c b/src/thread/pthread/SDL_sysmutex.c
index 5e3dd696e1..4b921e1a48 100644
--- a/src/thread/pthread/SDL_sysmutex.c
+++ b/src/thread/pthread/SDL_sysmutex.c
@@ -30,7 +30,7 @@ SDL_Mutex *SDL_CreateMutex(void)
     SDL_Mutex *mutex;
     pthread_mutexattr_t attr;
 
-    /* Allocate the structure */
+    // Allocate the structure
     mutex = (SDL_Mutex *)SDL_calloc(1, sizeof(*mutex));
     if (mutex) {
         pthread_mutexattr_init(&attr);
@@ -39,7 +39,7 @@ SDL_Mutex *SDL_CreateMutex(void)
 #elif defined(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX_NP)
         pthread_mutexattr_setkind_np(&attr, PTHREAD_MUTEX_RECURSIVE_NP);
 #else
-        /* No extra attributes necessary */
+        // No extra attributes necessary
 #endif
         if (pthread_mutex_init(&mutex->id, &attr) != 0) {
             SDL_SetError("pthread_mutex_init() failed");
@@ -60,116 +60,96 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
     }
 }
 
-/* Lock the mutex */
-int SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS // clang doesn't know about NULL mutexes
 {
+    if (mutex != NULL) {
 #ifdef FAKE_RECURSIVE_MUTEX
-    pthread_t this_thread;
-#endif
-
-    if (mutex == NULL) {
-        return 0;
-    }
-
-#ifdef FAKE_RECURSIVE_MUTEX
-    this_thread = pthread_self();
-    if (mutex->owner == this_thread) {
-        ++mutex->recursive;
-    } else {
-        /* The order of operations is important.
-           We set the locking thread id after we obtain the lock
-           so unlocks from other threads will fail.
-         */
-        if (pthread_mutex_lock(&mutex->id) == 0) {
+        pthread_t this_thread = pthread_self();
+        if (mutex->owner == this_thread) {
+            ++mutex->recursive;
+        } else {
+            /* The order of operations is important.
+               We set the locking thread id after we obtain the lock
+               so unlocks from other threads will fail.
+             */
+            const int rc = pthread_mutex_lock(&mutex->id);
+            SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
             mutex->owner = this_thread;
             mutex->recursive = 0;
-        } else {
-            return SDL_SetError("pthread_mutex_lock() failed");
         }
-    }
 #else
-    if (pthread_mutex_lock(&mutex->id) != 0) {
-        return SDL_SetError("pthread_mutex_lock() failed");
-    }
+        const int rc = pthread_mutex_lock(&mutex->id);
+        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
 #endif
-    return 0;
+    }
 }
 
 int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
-    int retval;
-    int result;
-#ifdef FAKE_RECURSIVE_MUTEX
-    pthread_t this_thread;
-#endif
+    int retval = 0;
 
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    retval = 0;
+    if (mutex != NULL) {
 #ifdef FAKE_RECURSIVE_MUTEX
-    this_thread = pthread_self();
-    if (mutex->owner == this_thread) {
-        ++mutex->recursive;
-    } else {
-        /* The order of operations is important.
-         We set the locking thread id after we obtain the lock
-         so unlocks from other threads will fail.
-         */
-        result = pthread_mutex_trylock(&mutex->id);
-        if (result == 0) {
-            mutex->owner = this_thread;
-            mutex->recursive = 0;
-        } else if (result == EBUSY) {
-            retval = SDL_MUTEX_TIMEDOUT;
+        pthread_t this_thread = pthread_self();
+        if (mutex->owner == this_thread) {
+            ++mutex->recursive;
         } else {
-            retval = SDL_SetError("pthread_mutex_trylock() failed");
+            /* The order of operations is important.
+             We set the locking thread id after we obtain the lock
+             so unlocks from other threads will fail.
+             */
+            const int result = pthread_mutex_trylock(&mutex->id);
+            if (result == 0) {
+                mutex->owner = this_thread;
+                mutex->recursive = 0;
+            } else if (result == EBUSY) {
+                retval = SDL_MUTEX_TIMEDOUT;
+            } else {
+                SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
+                retval = SDL_MUTEX_TIMEDOUT;
+            }
         }
-    }
 #else
-    result = pthread_mutex_trylock(&mutex->id);
-    if (result != 0) {
-        if (result == EBUSY) {
-            retval = SDL_MUTEX_TIMEDOUT;
-        } else {
-            retval = SDL_SetError("pthread_mutex_trylock() failed");
+        const int result = pthread_mutex_trylock(&mutex->id);
+        if (result != 0) {
+            if (result == EBUSY) {
+                retval = SDL_MUTEX_TIMEDOUT;
+            } else {
+                SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
+                retval = SDL_MUTEX_TIMEDOUT;
+            }
         }
-    }
 #endif
+    }
+
     return retval;
 }
 
-int SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS // clang doesn't know about NULL mutexes
 {
-    if (mutex == NULL) {
-        return 0;
-    }
-
+    if (mutex != NULL) {
 #ifdef FAKE_RECURSIVE_MUTEX
-    /* We can only unlock the mutex if we own it */
-    if (pthread_self() == mutex->owner) {
-        if (mutex->recursive) {
-            --mutex->recursive;
+        // We can only unlock the mutex if we own it
+        if (pthread_self() == mutex->owner) {
+            if (mutex->recursive) {
+                --mutex->recursive;
+            } else {
+                /* The order of operations is important.
+                   First reset the owner so another thread doesn't lock
+                   the mutex and set the ownership before we reset it,
+                   then release the lock semaphore.
+                 */
+                mutex->owner = 0;
+                pthread_mutex_unlock(&mutex->id);
+            }
         } else {
-            /* The order of operations is important.
-               First reset the owner so another thread doesn't lock
-               the mutex and set the ownership before we reset it,
-               then release the lock semaphore.
-             */
-            mutex->owner = 0;
-            pthread_mutex_unlock(&mutex->id);
+            return SDL_SetError("mutex not owned by this thread");
         }
-    } else {
-        return SDL_SetError("mutex not owned by this thread");
-    }
 
 #else
-    if (pthread_mutex_unlock(&mutex->id) != 0) {
-        return SDL_SetError("pthread_mutex_unlock() failed");
+        const int rc = pthread_mutex_unlock(&mutex->id);
+        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
+#endif // FAKE_RECURSIVE_MUTEX
     }
-#endif /* FAKE_RECURSIVE_MUTEX */
-
-    return 0;
 }
 
diff --git a/src/thread/pthread/SDL_sysrwlock.c b/src/thread/pthread/SDL_sysrwlock.c
index 3624d369e9..485264e85e 100644
--- a/src/thread/pthread/SDL_sysrwlock.c
+++ b/src/thread/pthread/SDL_sysrwlock.c
@@ -55,42 +55,36 @@ void SDL_DestroyRWLock(SDL_RWLock *rwlock)
     }
 }
 
-int SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (rwlock == NULL) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (pthread_rwlock_rdlock(&rwlock->id) != 0) {
-        return SDL_SetError("pthread_rwlock_rdlock() failed");
+    if (rwlock) {
+        const int rc = pthread_rwlock_rdlock(&rwlock->id);
+        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
     }
-    return 0;
 }
 
-int SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (rwlock == NULL) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (pthread_rwlock_wrlock(&rwlock->id) != 0) {
-        return SDL_SetError("pthread_rwlock_wrlock() failed");
+    if (rwlock) {
+        const int rc = pthread_rwlock_wrlock(&rwlock->id);
+        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
     }
-    return 0;
 }
 
 int SDL_TryLockRWLockForReading(SDL_RWLock *rwlock)
 {
     int retval = 0;
 
-    if (rwlock == NULL) {
-        retval = SDL_InvalidParamError("rwlock");
-    } else {
+    if (rwlock) {
         const int result = pthread_rwlock_tryrdlock(&rwlock->id);
         if (result != 0) {
-            if (result == EBUSY) {
-                retval = SDL_RWLOCK_TIMEDOUT;
-            } else {
-                retval = SDL_SetError("pthread_rwlock_tryrdlock() failed");
+            retval = SDL_RWLOCK_TIMEDOUT;
+            if (result != EBUSY) {
+                SDL_assert(!"Error trying to lock rwlock for reading");  // assume we're in a lot of trouble if this assert fails.
             }
         }
     }
+
     return retval;
 }
 
@@ -98,15 +92,12 @@ int SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock)
 {
     int retval = 0;
 
-    if (rwlock == NULL) {
-        retval = SDL_InvalidParamError("rwlock");
-    } else {
+    if (rwlock) {
         const int result = pthread_rwlock_trywrlock(&rwlock->id);
         if (result != 0) {
-            if (result == EBUSY) {
-                retval = SDL_RWLOCK_TIMEDOUT;
-            } else {
-                retval = SDL_SetError("pthread_rwlock_tryrdlock() failed");
+            retval = SDL_RWLOCK_TIMEDOUT;
+            if (result != EBUSY) {
+                SDL_assert(!"Error trying to lock rwlock for writing");  // assume we're in a lot of trouble if this assert fails.
             }
         }
     }
@@ -114,13 +105,11 @@ int SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock)
     return retval;
 }
 
-int SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (rwlock == NULL) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (pthread_rwlock_unlock(&rwlock->id) != 0) {
-        return SDL_SetError("pthread_rwlock_unlock() failed");
+    if (rwlock) {
+        const int rc = pthread_rwlock_unlock(&rwlock->id);
+        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
     }
-    return 0;
 }
 
diff --git a/src/thread/stdcpp/SDL_sysmutex.cpp b/src/thread/stdcpp/SDL_sysmutex.cpp
index 01181f09f5..3619c41398 100644
--- a/src/thread/stdcpp/SDL_sysmutex.cpp
+++ b/src/thread/stdcpp/SDL_sysmutex.cpp
@@ -27,74 +27,51 @@ extern "C" {
 #include <system_error>
 
 #include "SDL_sysmutex_c.h"
-#include <Windows.h>
+#include <windows.h>
 
-/* Create a mutex */
-extern "C" SDL_Mutex *
-SDL_CreateMutex(void)
+extern "C" SDL_Mutex * SDL_CreateMutex(void)
 {
-    /* Allocate and initialize the mutex */
+    // Allocate and initialize the mutex
     try {
         SDL_Mutex *mutex = new SDL_Mutex;
         return mutex;
     } catch (std::system_error &ex) {
         SDL_SetError("unable to create a C++ mutex: code=%d; %s", ex.code(), ex.what());
-        return NULL;
     } catch (std::bad_alloc &) {
         SDL_OutOfMemory();
-        return NULL;
     }
+    return NULL;
 }
 
-/* Free the mutex */
-extern "C" void
-SDL_DestroyMutex(SDL_Mutex *mutex)
+extern "C" void SDL_DestroyMutex(SDL_Mutex *mutex)
 {
     if (mutex != NULL) {
         delete mutex;
     }
 }
 
-/* Lock the mutex */
-extern "C" int
-SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+extern "C" void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    try {
-        mutex->cpp_mutex.lock();
-        return 0;
-    } catch (std::system_error &ex) {
-        return SDL_SetError("unable to lock a C++ mutex: code=%d; %s", ex.code(), ex.what());
+    if (mutex != NULL) {
+        try {
+            mutex->cpp_mutex.lock();
+        } catch (std::system_error &ex) {
+            SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
+            //return SDL_SetError("unable to lock a C++ mutex: code=%d; %s", ex.code(), ex.what());
+        }
     }
 }
 
-/* TryLock the mutex */
-int SDL_TryLockMutex(SDL_Mutex *mutex)
+extern "C" int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
-    int retval = 0;
-
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    if (mutex->cpp_mutex.try_lock() == false) {
-        retval = SDL_MUTEX_TIMEDOUT;
-    }
-    return retval;
+    return ((mutex == NULL) || mutex->cpp_mutex.try_lock()) ? 0 : SDL_MUTEX_TIMEDOUT;
 }
 
 /* Unlock the mutex */
-extern "C" int
-SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+extern "C" void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        mutex->cpp_mutex.unlock();
     }
-
-    mutex->cpp_mutex.unlock();
-    return 0;
 }
 
diff --git a/src/thread/stdcpp/SDL_sysrwlock.cpp b/src/thread/stdcpp/SDL_sysrwlock.cpp
index 72673cab06..e85f879a9c 100644
--- a/src/thread/stdcpp/SDL_sysrwlock.cpp
+++ b/src/thread/stdcpp/SDL_sysrwlock.cpp
@@ -30,10 +30,8 @@ struct SDL_RWLock
     SDL_threadID write_owner;
 };
 
-/* Create a rwlock */
 extern "C" SDL_RWLock *SDL_CreateRWLock(void)
 {
-    /* Allocate and initialize the rwlock */
     try {
         SDL_RWLock *rwlock = new SDL_RWLock;
         return rwlock;
@@ -46,7 +44,6 @@ extern "C" SDL_RWLock *SDL_CreateRWLock(void)
     }
 }
 
-/* Free the rwlock */
 extern "C" void SDL_DestroyRWLock(SDL_RWLock *rwlock)
 {
     if (rwlock != NULL) {
@@ -54,77 +51,64 @@ extern "C" void SDL_DestroyRWLock(SDL_RWLock *rwlock)
     }
 }
 
-/* Lock the rwlock */
-extern "C" int SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+extern "C" void SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
-    }
-
-    try {
-        rwlock->cpp_mutex.lock_shared();
-        return 0;
-    } catch (std::system_error &ex) {
-        return SDL_SetError("unable to lock a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+    if (rwlock) {
+        try {
+            rwlock->cpp_mutex.lock_shared();
+        } catch (std::system_error &ex) {
+            SDL_assert(!"Error trying to lock rwlock for reading");  // assume we're in a lot of trouble if this assert fails.
+            //return SDL_SetError("unable to lock a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+        }
     }
 }
 
-/* Lock the rwlock for writing */
-extern "C" int SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+extern "C" void SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS // clang doesn't know about NULL mutexes
 {
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
-    }
-
-    try {
-        rwlock->cpp_mutex.lock();
-        rwlock->write_owner = SDL_ThreadID();
-        return 0;
-    } catch (std::system_error &ex) {
-        return SDL_SetError("unable to lock a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+    if (rwlock) {
+        try {
+            rwlock->cpp_mutex.lock();
+            rwlock->write_owner = SDL_ThreadID();
+        } catch (std::system_error &ex) {
+            SDL_assert(!"Error trying to lock rwlock for writing");  // assume we're in a lot of trouble if this assert fails.
+            //return SDL_SetError("unable to lock a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+        }
     }
 }
 
-/* TryLock the rwlock for reading */
-int SDL_TryLockRWLockForReading(SDL_RWLock *rwlock)
+extern "C" int SDL_TryLockRWLockForReading(SDL_RWLock *rwlock)
 {
     int retval = 0;
-
-    if (!rwlock) {
-        retval = SDL_InvalidParamError("rwlock");
-    } else if (rwlock->cpp_mutex.try_lock_shared() == false) {
-        retval = SDL_RWLOCK_TIMEDOUT;
+    if (rwlock) {
+        if (rwlock->cpp_mutex.try_lock_shared() == false) {
+            retval = SDL_RWLOCK_TIMEDOUT;
+        }
     }
     return retval;
 }
 
-/* TryLock the rwlock for writing */
-int SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock)
+extern "C" int SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock)
 {
     int retval = 0;
-
-    if (!rwlock) {
-        retval = SDL_InvalidParamError("rwlock");
-    } else if (rwlock->cpp_mutex.try_lock() == false) {
-        retval = SDL_RWLOCK_TIMEDOUT;
-    } else {
-        rwlock->write_owner = SDL_ThreadID();
+    if (rwlock) {
+        if (rwlock->cpp_mutex.try_lock() == false) {
+            retval = SDL_RWLOCK_TIMEDOUT;
+        } else {
+            rwlock->write_owner = SDL_ThreadID();
+        }
     }
     return retval;
 }
 
-/* Unlock the rwlock */
-extern "C" int
-SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+extern "C" void SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (!rwlock) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (rwlock->write_owner == SDL_ThreadID()) {
-        rwlock->write_owner = 0;
-        rwlock->cpp_mutex.unlock();
-    } else {
-        rwlock->cpp_mutex.unlock_shared();
+    if (rwlock) {
+        if (rwlock->write_owner == SDL_ThreadID()) {
+            rwlock->write_owner = 0;
+            rwlock->cpp_mutex.unlock();
+        } else {
+            rwlock->cpp_mutex.unlock_shared();
+        }
     }
-    return 0;
 }
 
diff --git a/src/thread/vita/SDL_sysmutex.c b/src/thread/vita/SDL_sysmutex.c
index 5e5ee47f9f..1bc27780e8 100644
--- a/src/thread/vita/SDL_sysmutex.c
+++ b/src/thread/vita/SDL_sysmutex.c
@@ -32,24 +32,20 @@ struct SDL_Mutex
     SceKernelLwMutexWork lock;
 };
 
-/* Create a mutex */
 SDL_Mutex *SDL_CreateMutex(void)
 {
-    SDL_Mutex *mutex = NULL;
-    SceInt32 res = 0;
-
-    /* Allocate mutex memory */
-    mutex = (SDL_Mutex *)SDL_malloc(sizeof(*mutex));
+    SDL_Mutex *mutex = (SDL_Mutex *)SDL_malloc(sizeof(*mutex));
     if (mutex != NULL) {
-
-        res = sceKernelCreateLwMutex(
-            &mutex->lock,
-            "SDL mutex",
-            SCE_KERNEL_MUTEX_ATTR_RECURSIVE,
-            0,
-            NULL);
+        const SceInt32 res = sceKernelCreateLwMutex(
+                                &mutex->lock,
+                                "SDL mutex",
+                                SCE_KERNEL_MUTEX_ATTR_RECURSIVE,
+                                0,
+                                NULL);
 
         if (res < 0) {
+            SDL_free(mutex);
+            mutex = NULL;
             SDL_SetError("Error trying to create mutex: %x", res);
         }
     } else {
@@ -58,7 +54,6 @@ SDL_Mutex *SDL_CreateMutex(void)
     return mutex;
 }
 
-/* Free the mutex */
 void SDL_DestroyMutex(SDL_Mutex *mutex)
 {
     if (mutex != NULL) {
@@ -67,28 +62,16 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
     }
 }
 
-/* Lock the mutex */
-int SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    SceInt32 res = 0;
-
-    if (mutex == NULL) {
-        return 0;
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        const SceInt32 res = sceKernelLockLwMutex(&mutex->lock, 1, NULL);
+        SDL_assert(res == SCE_KERNEL_OK);  // assume we're in a lot of trouble if this assert fails.
     }
-
-    res = sceKernelLockLwMutex(&mutex->lock, 1, NULL);
-    if (res != SCE_KERNEL_OK) {
-        return SDL_SetError("Error trying to lock mutex: %x", res);
-    }
-
-    return 0;
-#endif /* SDL_THREADS_DISABLED */
+#endif // SDL_THREADS_DISABLED
 }
 
-/* Try to lock the mutex */
 int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
 #ifdef SDL_THREADS_DISABLED
@@ -102,40 +85,24 @@ int SDL_TryLockMutex(SDL_Mutex *mutex)
 
     res = sceKernelTryLockLwMutex(&mutex->lock, 1);
     switch (res) {
-    case SCE_KERNEL_OK:
-        return 0;
-        break;
-    case SCE_KERNEL_ERROR_MUTEX_FAILED_TO_OWN:
-        return SDL_MUTEX_TIMEDOUT;
-        break;
-    default:
-        return SDL_SetError("Error trying to lock mutex: %x", res);
-        break;
+    case SCE_KERNEL_OK: return 0;
+    case SCE_KERNEL_ERROR_MUTEX_FAILED_TO_OWN: return SDL_MUTEX_TIMEDOUT;
+    default: break;
     }
 
-    return -1;
-#endif /* SDL_THREADS_DISABLED */
+    SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
+    return SDL_MUTEX_TIMEDOUT;
+#endif // SDL_THREADS_DISABLED
 }
 
-/* Unlock the mutex */
-int SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-#ifdef SDL_THREADS_DISABLED
-    return 0;
-#else
-    SceInt32 res = 0;
-
-    if (mutex == NULL) {
-        return 0;
+#ifndef SDL_THREADS_DISABLED
+    if (mutex != NULL) {
+        const SceInt32 res = sceKernelUnlockLwMutex(&mutex->lock, 1);
+        SDL_assert(res == SCE_KERNEL_OK);  // assume we're in a lot of trouble if this assert fails.
     }
-
-    res = sceKernelUnlockLwMutex(&mutex->lock, 1);
-    if (res != 0) {
-        return SDL_SetError("Error trying to unlock mutex: %x", res);
-    }
-
-    return 0;
-#endif /* SDL_THREADS_DISABLED */
+#endif // SDL_THREADS_DISABLED
 }
 
-#endif /* SDL_THREAD_VITA */
+#endif // SDL_THREAD_VITA
diff --git a/src/thread/windows/SDL_sysmutex.c b/src/thread/windows/SDL_sysmutex.c
index 16cc81f93b..d70aa1be16 100644
--- a/src/thread/windows/SDL_sysmutex.c
+++ b/src/thread/windows/SDL_sysmutex.c
@@ -76,12 +76,11 @@ static void SDL_DestroyMutex_srw(SDL_Mutex *mutex)
     SDL_free(mutex);
 }
 
-static int SDL_LockMutex_srw(SDL_Mutex *_mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_LockMutex_srw(SDL_Mutex *_mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_mutex_srw *mutex = (SDL_mutex_srw *)_mutex;
-    DWORD this_thread;
+    const DWORD this_thread = GetCurrentThreadId();
 
-    this_thread = GetCurrentThreadId();
     if (mutex->owner == this_thread) {
         ++mutex->count;
     } else {
@@ -94,16 +93,14 @@ static int SDL_LockMutex_srw(SDL_Mutex *_mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /*
         mutex->owner = this_thread;
         mutex->count = 1;
     }
-    return 0;
 }
 
 static int SDL_TryLockMutex_srw(SDL_Mutex *_mutex)
 {
     SDL_mutex_srw *mutex = (SDL_mutex_srw *)_mutex;
-    DWORD this_thread;
+    const DWORD this_thread = GetCurrentThreadId();
     int retval = 0;
 
-    this_thread = GetCurrentThreadId();
     if (mutex->owner == this_thread) {
         ++mutex->count;
     } else {
@@ -118,7 +115,7 @@ static int SDL_TryLockMutex_srw(SDL_Mutex *_mutex)
     return retval;
 }
 
-static int SDL_UnlockMutex_srw(SDL_Mutex *_mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_UnlockMutex_srw(SDL_Mutex *_mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_mutex_srw *mutex = (SDL_mutex_srw *)_mutex;
 
@@ -128,10 +125,8 @@ static int SDL_UnlockMutex_srw(SDL_Mutex *_mutex) SDL_NO_THREAD_SAFETY_ANALYSIS
             pReleaseSRWLockExclusive(&mutex->srw);
         }
     } else {
-        return SDL_SetError("mutex not owned by this thread");
+        SDL_assert(!"mutex not owned by this thread");  // undefined behavior...!
     }
-
-    return 0;
 }
 
 static const SDL_mutex_impl_t SDL_mutex_impl_srw = {
@@ -147,16 +142,12 @@ static const SDL_mutex_impl_t SDL_mutex_impl_srw = {
  * Fallback Mutex implementation using Critical Sections (before Win 7)
  */
 
-/* Create a mutex */
 static SDL_Mutex *SDL_CreateMutex_cs(void)
 {
-    SDL_mutex_cs *mutex;
-
-    /* Allocate mutex memory */
-    mutex = (SDL_mutex_cs *)SDL_malloc(sizeof(*mutex));
+    SDL_mutex_cs *mutex = (SDL_mutex_cs *)SDL_malloc(sizeof(*mutex));
     if (mutex != NULL) {
-        /* Initialize */
-        /* On SMP systems, a non-zero spin count generally helps performance */
+        // Initialize
+        // On SMP systems, a non-zero spin count generally helps performance
 #ifdef __WINRT__
         InitializeCriticalSectionEx(&mutex->cs, 2000, 0);
 #else
@@ -168,43 +159,29 @@ static SDL_Mutex *SDL_CreateMutex_cs(void)
     return (SDL_Mutex *)mutex;
 }
 
-/* Free the mutex */
 static void SDL_DestroyMutex_cs(SDL_Mutex *mutex_)
 {
     SDL_mutex_cs *mutex = (SDL_mutex_cs *)mutex_;
-
     DeleteCriticalSection(&mutex->cs);
     SDL_free(mutex);
 }
 
-/* Lock the mutex */
-static int SDL_LockMutex_cs(SDL_Mutex *mutex_) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_LockMutex_cs(SDL_Mutex *mutex_) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_mutex_cs *mutex = (SDL_mutex_cs *)mutex_;
-
     EnterCriticalSection(&mutex->cs);
-    return 0;
 }
 
-/* TryLock the mutex */
 static int SDL_TryLockMutex_cs(SDL_Mutex *mutex_)
 {
     SDL_mutex_cs *mutex = (SDL_mutex_cs *)mutex_;
-    int retval = 0;
-
-    if (TryEnterCriticalSection(&mutex->cs) == 0) {
-        retval = SDL_MUTEX_TIMEDOUT;
-    }
-    return retval;
+    return (TryEnterCriticalSection(&mutex->cs) == 0) ? SDL_MUTEX_TIMEDOUT : 0;
 }
 
-/* Unlock the mutex */
-static int SDL_UnlockMutex_cs(SDL_Mutex *mutex_) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_UnlockMutex_cs(SDL_Mutex *mutex_) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_mutex_cs *mutex = (SDL_mutex_cs *)mutex_;
-
     LeaveCriticalSection(&mutex->cs);
-    return 0;
 }
 
 static const SDL_mutex_impl_t SDL_mutex_impl_cs = {
@@ -223,22 +200,22 @@ static const SDL_mutex_impl_t SDL_mutex_impl_cs = {
 SDL_Mutex *SDL_CreateMutex(void)
 {
     if (SDL_mutex_impl_active.Create == NULL) {
-        /* Default to fallback implementation */
+        // Default to fallback implementation
         const SDL_mutex_impl_t *impl = &SDL_mutex_impl_cs;
 
         if (!SDL_GetHintBoolean(SDL_HINT_WINDOWS_FORCE_MUTEX_CRITICAL_SECTIONS, SDL_FALSE)) {
 #ifdef __WINRT__
-            /* Link statically on this platform */
+            // Link statically on this platform
             impl = &SDL_mutex_impl_srw;
 #else
-            /* Try faster implementation for Windows 7 and newer */
+            // Try faster implementation for Windows 7 and newer
             HMODULE kernel32 = GetModuleHandle(TEXT("kernel32.dll"));
             if (kernel32) {
-                /* Requires Vista: */
+                // Requires Vista:
                 pInitializeSRWLock = (pfnInitializeSRWLock)GetProcAddress(kernel32, "InitializeSRWLock");
                 pReleaseSRWLockExclusive = (pfnReleaseSRWLockExclusive)GetProcAddress(kernel32, "ReleaseSRWLockExclusive");
                 pAcquireSRWLockExclusive = (pfnAcquireSRWLockExclusive)GetProcAddress(kernel32, "AcquireSRWLockExclusive");
-                /* Requires 7: */
+                // Requires 7:
                 pTryAcquireSRWLockExclusive = (pfnTryAcquireSRWLockExclusive)GetProcAddress(kernel32, "TryAcquireSRWLockExclusive");
                 if (pInitializeSRWLock && pReleaseSRWLockExclusive && pAcquireSRWLockExclusive && pTryAcquireSRWLockExclusive) {
                     impl = &SDL_mutex_impl_srw;
@@ -247,7 +224,7 @@ SDL_Mutex *SDL_CreateMutex(void)
 #endif
         }
 
-        /* Copy instead of using pointer to save one level of indirection */
+        // Copy instead of using pointer to save one level of indirection
         SDL_copyp(&SDL_mutex_impl_active, impl);
     }
     return SDL_mutex_impl_active.Create();
@@ -260,31 +237,23 @@ void SDL_DestroyMutex(SDL_Mutex *mutex)
     }
 }
 
-int SDL_LockMutex(SDL_Mutex *mutex)
+void SDL_LockMutex(SDL_Mutex *mutex)
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        SDL_mutex_impl_active.Lock(mutex);
     }
-
-    return SDL_mutex_impl_active.Lock(mutex);
 }
 
 int SDL_TryLockMutex(SDL_Mutex *mutex)
 {
-    if (mutex == NULL) {
-        return 0;
-    }
-
-    return SDL_mutex_impl_active.TryLock(mutex);
+    return mutex ? SDL_mutex_impl_active.TryLock(mutex) : 0;
 }
 
-int SDL_UnlockMutex(SDL_Mutex *mutex)
+void SDL_UnlockMutex(SDL_Mutex *mutex)
 {
-    if (mutex == NULL) {
-        return 0;
+    if (mutex != NULL) {
+        SDL_mutex_impl_active.Unlock(mutex);
     }
-
-    return SDL_mutex_impl_active.Unlock(mutex);
 }
 
-#endif /* SDL_THREAD_WINDOWS */
+#endif // SDL_THREAD_WINDOWS
diff --git a/src/thread/windows/SDL_sysmutex_c.h b/src/thread/windows/SDL_sysmutex_c.h
index 5a04e143e4..d495ffe49b 100644
--- a/src/thread/windows/SDL_sysmutex_c.h
+++ b/src/thread/windows/SDL_sysmutex_c.h
@@ -23,9 +23,9 @@
 #include "../../core/windows/SDL_windows.h"
 
 typedef SDL_Mutex *(*pfnSDL_CreateMutex)(void);
-typedef int (*pfnSDL_LockMutex)(SDL_Mutex *);
+typedef void (*pfnSDL_LockMutex)(SDL_Mutex *);
 typedef int (*pfnSDL_TryLockMutex)(SDL_Mutex *);
-typedef int (*pfnSDL_UnlockMutex)(SDL_Mutex *);
+typedef void (*pfnSDL_UnlockMutex)(SDL_Mutex *);
 typedef void (*pfnSDL_DestroyMutex)(SDL_Mutex *);
 
 typedef enum
diff --git a/src/thread/windows/SDL_sysrwlock_srw.c b/src/thread/windows/SDL_sysrwlock_srw.c
index bec3cb07df..c22eecae8e 100644
--- a/src/thread/windows/SDL_sysrwlock_srw.c
+++ b/src/thread/windows/SDL_sysrwlock_srw.c
@@ -57,11 +57,11 @@ static pfnTryAcquireSRWLockExclusive pTryAcquireSRWLockExclusive = NULL;
 
 typedef SDL_RWLock *(*pfnSDL_CreateRWLock)(void);
 typedef void (*pfnSDL_DestroyRWLock)(SDL_RWLock *);
-typedef int (*pfnSDL_LockRWLockForReading)(SDL_RWLock *);
-typedef int (*pfnSDL_LockRWLockForWriting)(SDL_RWLock *);
+typedef void (*pfnSDL_LockRWLockForReading)(SDL_RWLock *);
+typedef void (*pfnSDL_LockRWLockForWriting)(SDL_RWLock *);
 typedef int (*pfnSDL_TryLockRWLockForReading)(SDL_RWLock *);
 typedef int (*pfnSDL_TryLockRWLockForWriting)(SDL_RWLock *);
-typedef int (*pfnSDL_UnlockRWLock)(SDL_RWLock *);
+typedef void (*pfnSDL_UnlockRWLock)(SDL_RWLock *);
 
 typedef struct SDL_rwlock_impl_t
 {
@@ -104,35 +104,28 @@ static void SDL_DestroyRWLock_srw(SDL_RWLock *_rwlock)
     }
 }
 
-static int SDL_LockRWLockForReading_srw(SDL_RWLock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_LockRWLockForReading_srw(SDL_RWLock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
-    if (rwlock == NULL) {
-        return SDL_InvalidParamError("rwlock");
+    if (rwlock != NULL) {
+        pAcquireSRWLockShared(&rwlock->srw);
     }
-    pAcquireSRWLockShared(&rwlock->srw);
-    return 0;
 }
 
-static int SDL_LockRWLockForWriting_srw(SDL_RWLock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_LockRWLockForWriting_srw(SDL_RWLock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
-    if (rwlock == NULL) {
-        return SDL_InvalidParamError("rwlock");
+    if (rwlock != NULL) {
+        pAcquireSRWLockExclusive(&rwlock->srw);
+        rwlock->write_owner = SDL_ThreadID();
     }
-    pAcquireSRWLockExclusive(&rwlock->srw);
-    rwlock->write_owner = SDL_ThreadID();
-    return 0;
 }
 
 static int SDL_TryLockRWLockForReading_srw(SDL_RWLock *_rwlock)
 {
     SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
     int retval = 0;
-
-    if (rwlock == NULL) {
-        retval = SDL_InvalidParamError("rwlock");
-    } else {
+    if (rwlock != NULL) {
         retval = pTryAcquireSRWLockShared(&rwlock->srw) ? 0 : SDL_RWLOCK_TIMEDOUT;
     }
     return retval;
@@ -142,27 +135,23 @@ static int SDL_TryLockRWLockForWriting_srw(SDL_RWLock *_rwlock)
 {
     SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
     int retval = 0;
-
-    if (rwlock == NULL) {
-        retval = SDL_InvalidParamError("rwlock");
-    } else {
+    if (rwlock != NULL) {
         retval = pTryAcquireSRWLockExclusive(&rwlock->srw) ? 0 : SDL_RWLOCK_TIMEDOUT;
     }
     return retval;
 }
 
-static int SDL_UnlockRWLock_srw(SDL_RWLock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+static void SDL_UnlockRWLock_srw(SDL_RWLock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
     SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
-    if (rwlock == NULL) {
-        return SDL_InvalidParamError("rwlock");
-    } else if (rwlock->write_owner == SDL_ThreadID()) {
-        rwlock->write_owner = 0;
-        pReleaseSRWLockExclusive(&rwlock->srw);
-    } else {
-        pReleaseSRWLockShared(&rwlock->srw);
+    if (rwlock != NULL) {
+        if (rwlock->write_owner == SDL_ThreadID()) {
+            rwlock->write_owner = 0;
+            pReleaseSRWLockExclusive(&rwlock->srw);
+        } else {
+            pReleaseSRWLockShared(&rwlock->srw);
+        }
     }
-    return 0;
 }
 
 static const SDL_rwlock_impl_t SDL_rwlock_impl_srw = {
@@ -234,47 +223,34 @@ void SDL_DestroyRWLock(SDL_RWLock *rwlock)
     }
 }
 
-int SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (rwlock == NULL) {
-        return 0;
+    if (rwlock != NULL) {
+        SDL_rwlock_impl_active.LockForReading(rwlock);
     }
-
-    return SDL_rwlock_impl_active.LockForReading(rwlock);
 }
 
-int SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (rwlock == NULL) {
-        return 0;
+    if (rwlock != NULL) {
+        SDL_rwlock_impl_active.LockForWriting(rwlock);
     }
-
-    return SDL_rwlock_impl_active.LockForWriting(rwlock);
 }
 
 int SDL_TryLockRWLockForReading(SDL_RWLock *rwlock)
 {
-    if (rwlock == NULL) {
-        return 0;
-    }
-
-    return SDL_rwlock_impl_active.TryLockForReading(rwlock);
+    return rwlock ? SDL_rwlock_impl_active.TryLockForReading(rwlock) : 0;
 }
 
 int SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock)
 {
-    if (rwlock == NULL) {
-        return 0;
-    }
-
-    return SDL_rwlock_impl_active.TryLockForWriting(rwlock);
+    return rwlock ? SDL_rwlock_impl_active.TryLockForWriting(rwlock) : 0;
 }
 
-int SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+void SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
 {
-    if (rwlock == NULL) {
-        return 0;
+    if (rwlock != NULL) {
+        SDL_rwlock_impl_active.Unlock(rwlock);
     }
-
-    return SDL_rwlock_impl_active.Unlock(rwlock);
 }
+
diff --git a/test/testlock.c b/test/testlock.c
index e0413d87d9..edf259ad46 100644
--- a/test/testlock.c
+++ b/test/testlock.c
@@ -80,17 +80,12 @@ Run(void *data)
     SDL_Log("Thread %lu: starting up", SDL_ThreadID());
     while (!SDL_AtomicGet(&doterminate)) {
         SDL_Log("Thread %lu: ready to work\n", SDL_ThreadID());
-        if (SDL_LockMutex(mutex) < 0) {
-            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't lock mutex: %s", SDL_GetError());
-            exit(1);
-        }
+        SDL_LockMutex(mutex);
         SDL_Log("Thread %lu: start work!\n", SDL_ThreadID());
         SDL_Delay(1 * worktime);
         SDL_Log("Thread %lu: work done!\n", SDL_ThreadID());
-        if (SDL_UnlockMutex(mutex) < 0) {
-            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't unlock mutex: %s", SDL_GetError());
-            exit(1);
-        }
+        SDL_UnlockMutex(mutex);
+
         /* If this sleep isn't done, then threads may starve */
         SDL_Delay(10);
     }
diff --git a/test/testrwlock.c b/test/testrwlock.c
index cada79e559..7952a2ef74 100644
--- a/test/testrwlock.c
+++ b/test/testrwlock.c
@@ -33,22 +33,21 @@ static void DoWork(const int workticks)  /* "Work" */
     const SDL_threadID tid = SDL_ThreadID();
     const SDL_bool is_reader = tid != mainthread;
     const char *typestr = is_reader ? "Reader" : "Writer";
-    int rc;
 
     SDL_Log("%s Thread %lu: ready to work\n", typestr, (unsigned long) tid);
-    rc = is_reader ? SDL_LockRWLockForReading(rwlock) : SDL_LockRWLockForWriting(rwlock);
-    if (rc < 0) {
-        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "%s Thread %lu: Couldn't lock rwlock: %s", typestr, (unsigned long) tid, SDL_GetError());
+    if (is_reader) {
+        SDL_LockRWLockForReading(rwlock);
     } else {
-        SDL_Log("%s Thread %lu: start work!\n", typestr, (unsigned long) tid);
-        SDL_Delay(workticks);
-        SDL_Log("%s Thread %lu: work done!\n", typestr, (unsigned long) tid);
-        if (SDL_UnlockRWLock(rwlock) < 0) {
-            SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "%s Thread %lu: Couldn't unlock rwlock: %s", typestr, (unsigned long) tid, SDL_GetError());
-        }
-        /* If this sleep isn't done, then threads may starve */
-        SDL_Delay(10);
+        SDL_LockRWLockForWriting(rwlock);
     }
+
+    SDL_Log("%s Thread %lu: start work!\n", typestr, (unsigned long) tid);
+    SDL_Delay(workticks);
+    SDL_Log("%s Thread %lu: work done!\n", typestr, (unsigned long) tid);
+    SDL_UnlockRWLock(rwlock);
+
+    /* If this sleep isn't done, then threads may starve */
+    SDL_Delay(10);
 }
 
 static int SDLCALL