diff --git a/headers/posix/string.h b/headers/posix/string.h
index 81992c019f..f7e4ab4b1f 100644
--- a/headers/posix/string.h
+++ b/headers/posix/string.h
@@ -22,6 +22,10 @@ extern void		*memccpy(void *dest, const void *source, int stopByte, size_t lengt
 extern void		*memmove(void *dest, const void *source, size_t length);
 extern void		*memset(void *dest, int value, size_t length);
 
+#ifdef __USE_GNU
+extern void		*memrchr(const void *source, int value, size_t length);
+#endif
+
 /* string functions */
 extern char		*strcpy(char *dest, const char *source);
 extern char		*strncpy(char *dest, const char *source, size_t length);
@@ -36,8 +40,9 @@ extern char		*strchr(const char *string, int character);
 extern char		*strrchr(const char *string, int character);
 extern char		*strstr(const char *string, const char *searchString);
 
+#ifdef __USE_GNU
 extern char		*strchrnul(const char *string, int character);
-	/* this is a GNU extension */
+#endif
 
 extern char		*strpbrk(const char *string, const char *set);
 extern char		*strtok(char *string, const char *set);