diff --git a/wolfssl/wolfcrypt/types.h b/wolfssl/wolfcrypt/types.h
index 37a982bf8..c060e1f9b 100644
--- a/wolfssl/wolfcrypt/types.h
+++ b/wolfssl/wolfcrypt/types.h
@@ -332,7 +332,7 @@
         #elif defined(USE_WINDOWS_API) || defined(FREERTOS_TCP_WINSIM)
 	        #define XSTRNCASECMP(s1,s2,n) _strnicmp((s1),(s2),(n))
         #else
-            #if (defined(HAVE_STRINGS_H) || defined(WOLF_C99)) && \
+            #if defined(HAVE_STRINGS_H) && defined(WOLF_C99) && \
                 !defined(WOLFSSL_SGX)
                 #include <strings.h>
             #endif
diff --git a/wolfssl/wolfcrypt/wc_port.h b/wolfssl/wolfcrypt/wc_port.h
index 5fc6e49d5..9a6333a1f 100644
--- a/wolfssl/wolfcrypt/wc_port.h
+++ b/wolfssl/wolfcrypt/wc_port.h
@@ -33,8 +33,10 @@
     extern "C" {
 #endif
 
-/* detect C99 */
-#if !defined(WOLF_C99) && defined(__STDC_VERSION__) && !defined(WOLFSSL_ARDUINO)
+/* Detect if compiler supports C99. "NO_WOLF_C99" can be defined in
+ * user_settings.h to disable checking for C99 support. */
+#if !defined(WOLF_C99) && defined(__STDC_VERSION__) && \
+    !defined(WOLFSSL_ARDUINO) && !defined(NO_WOLF_C99)
     #if __STDC_VERSION__ >= 199901L
         #define WOLF_C99
     #endif