diff --git a/src/auth_passwd.c b/src/auth_passwd.c
index e92a41c..53a4636 100644
--- a/src/auth_passwd.c
+++ b/src/auth_passwd.c
@@ -24,6 +24,8 @@
 
 #include "alock.h"
 
+#define _XOPEN_SOURCE
+
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <errno.h>