diff --git a/c-programming/mem/safe_mem.h b/c-programming/mem/safe_mem.h
index d426a7f..49c95b5 100644
--- a/c-programming/mem/safe_mem.h
+++ b/c-programming/mem/safe_mem.h
@@ -16,6 +16,7 @@
 #ifndef _SAFE_MEM_H
 #define _SAFE_MEM_H
 
+#define __STDC_WANT_LIB_EXT1__ 1
 #include <stdlib.h>
 
 typedef unsigned char byte;