diff --git a/tools/probe-req.c b/tools/probe-req.c
index 7ec8e3af..86fe48ee 100644
--- a/tools/probe-req.c
+++ b/tools/probe-req.c
@@ -24,6 +24,7 @@
 #include <config.h>
 #endif
 
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/types.h>