diff --git a/library/cipher.c b/library/cipher.c
index 85c74aba1..0d1258bc9 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -260,7 +260,7 @@ int cipher_init_ctx( cipher_context_t *ctx, const cipher_info_t *cipher_info )
     if( NULL == cipher_info || NULL == ctx )
         return POLARSSL_ERR_CIPHER_BAD_INPUT_DATA;
 
-    memset( ctx, 0, sizeof( ctx ) );
+    memset( ctx, 0, sizeof( cipher_context_t ) );
 
     if( NULL == ( ctx->cipher_ctx = cipher_info->base->ctx_alloc_func() ) )
         return POLARSSL_ERR_CIPHER_ALLOC_FAILED;
diff --git a/library/md.c b/library/md.c
index d15bf1dca..96065c95f 100644
--- a/library/md.c
+++ b/library/md.c
@@ -152,11 +152,10 @@ const md_info_t *md_info_from_type( md_type_t md_type )
 
 int md_init_ctx( md_context_t *ctx, const md_info_t *md_info )
 {
-    if( md_info == NULL )
+    if( md_info == NULL || ctx == NULL )
         return POLARSSL_ERR_MD_BAD_INPUT_DATA;
 
-    if( ctx == NULL || ctx->md_ctx != NULL )
-        return POLARSSL_ERR_MD_BAD_INPUT_DATA;
+    memset( ctx, 0, sizeof( md_context_t ) );
 
     if( ( ctx->md_ctx = md_info->ctx_alloc_func() ) == NULL )
         return POLARSSL_ERR_MD_ALLOC_FAILED;