diff --git a/shared/libc/string0.c b/shared/libc/string0.c
index b0a2620300..5b48e705e5 100644
--- a/shared/libc/string0.c
+++ b/shared/libc/string0.c
@@ -26,6 +26,7 @@
 
 #include <stdint.h>
 #include <stddef.h>
+#undef _FORTIFY_SOURCE
 #include <string.h>
 
 #include "py/mpconfig.h"
@@ -75,15 +76,6 @@ void *memcpy(void *dst, const void *src, size_t n) {
     return dst;
 }
 
-// CIRCUITPY-CHANGE: extern
-extern void *__memcpy_chk(void *dest, const void *src, size_t len, size_t slen);
-void *__memcpy_chk(void *dest, const void *src, size_t len, size_t slen) {
-    if (len > slen) {
-        return NULL;
-    }
-    return memcpy(dest, src, len);
-}
-
 void *memmove(void *dest, const void *src, size_t n) {
     if (src < dest && (uint8_t*)dest < (const uint8_t*)src + n) {
         // need to copy backwards