diff --git a/manual/examples/select.c b/manual/examples/select.c
index 341b65f11d..db138c3ecd 100644
--- a/manual/examples/select.c
+++ b/manual/examples/select.c
@@ -16,6 +16,7 @@
 */
 
 /*@group*/
+#define _GNU_SOURCE 1
 #include <errno.h>
 #include <stdio.h>
 #include <unistd.h>