diff --git a/library/aesni.h b/library/aesni.h
index a054cfd5c..97b3abbef 100644
--- a/library/aesni.h
+++ b/library/aesni.h
@@ -59,9 +59,14 @@
 #define MBEDTLS_AESNI_HAVE_INTRINSICS
 #endif
 
-/* Choose the implementation of AESNI, if one is available. */
-#undef MBEDTLS_AESNI_HAVE_CODE
-/* Favor the intrinsics-based implementation if it's available, for better
+/* Normally MBEDTLS_AESNI_HAVE_CODE is automatically set below. It may be
+ * set from all.sh to ensure coverage of both asm and intrinsics, in which
+ * case we do not over-ride it. */
+#if !defined(MBEDTLS_AESNI_HAVE_CODE)
+
+/* Choose the implementation of AESNI, if one is available.
+ *
+ * Favor the intrinsics-based implementation if it's available, for better
  * maintainability.
  * Performance is about the same (see #7380).
  * In the long run, we will likely remove the assembly implementation. */
@@ -70,6 +75,7 @@
 #elif defined(MBEDTLS_HAVE_X86_64)
 #define MBEDTLS_AESNI_HAVE_CODE 1 // via assembly
 #endif
+#endif /* !defined(MBEDTLS_AESNI_HAVE_CODE) */
 
 #if defined(MBEDTLS_AESNI_HAVE_CODE)