diff --git a/client/known-networks.c b/client/known-networks.c
index b2023e35..8634aca2 100644
--- a/client/known-networks.c
+++ b/client/known-networks.c
@@ -24,8 +24,7 @@
 #include <config.h>
 #endif
 
-#define _XOPEN_SOURCE 700
-
+#define _XOPEN_SOURCE
 #include <time.h>
 #include <ell/ell.h>