diff --git a/Documentation/networking/timestamping/txtimestamp.c b/Documentation/networking/timestamping/txtimestamp.c
index 8778e684d482..05694febc238 100644
--- a/Documentation/networking/timestamping/txtimestamp.c
+++ b/Documentation/networking/timestamping/txtimestamp.c
@@ -30,6 +30,8 @@
  * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#define _GNU_SOURCE
+
 #include <arpa/inet.h>
 #include <asm/types.h>
 #include <error.h>