diff --git a/crypt.c b/crypt.c
--- a/crypt.c
+++ b/crypt.c
@@ -3,6 +3,8 @@
  * Copyright (C) 2008 Markus Broeker
  */
 
+#define _XOPEN_SOURCE 500
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>