diff --git a/src/x11/window-props.c b/src/x11/window-props.c
index adaab0eba..48454befe 100644
--- a/src/x11/window-props.c
+++ b/src/x11/window-props.c
@@ -34,7 +34,7 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
-#define _XOPEN_SOURCE 500 /* for gethostname() */
+#define _XOPEN_SOURCE 600 /* for gethostname() */
 
 #include "config.h"