diff --git a/src/x11/window-props.c b/src/x11/window-props.c
index adaab0eba1fb543330b8a745c75d9ccac3e734e2..48454befe8c6836757c2fe3f74bb8d4020e402e6 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"