diff --git a/libavdevice/x11grab.c b/libavdevice/x11grab.c
index ff37d762a6..60993276f5 100644
--- a/libavdevice/x11grab.c
+++ b/libavdevice/x11grab.c
@@ -35,6 +35,8 @@
  * and Edouard Gomez <ed.gomez@free.fr>.
  */
 
+#define _XOPEN_SOURCE 600
+
 #include "config.h"
 #include "libavformat/avformat.h"
 #include <time.h>