diff --git a/src/eap-md5.c b/src/eap-md5.c
index fcca550c..5cd0e01c 100644
--- a/src/eap-md5.c
+++ b/src/eap-md5.c
@@ -24,8 +24,10 @@
 #include <config.h>
 #endif
 
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <errno.h>
+#include <string.h>
 #include <ell/ell.h>
 
 #include "src/missing.h"