diff --git a/mnexec.c b/mnexec.c
index c30b4a6..ea8fb6f 100644
--- a/mnexec.c
+++ b/mnexec.c
@@ -13,6 +13,7 @@
  * Partially based on public domain setsid(1)
 */
 
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <linux/sched.h>
 #include <unistd.h>