diff --git a/btrfsck.c b/btrfsck.c
index eb8e38e0..e5be0319 100644
--- a/btrfsck.c
+++ b/btrfsck.c
@@ -17,9 +17,9 @@
  */
 
 #define _XOPEN_SOURCE 500
+#define _GNU_SOURCE 1
 #include <stdio.h>
 #include <stdlib.h>
-#define __USE_GNU
 #include <fcntl.h>
 #include "kerncompat.h"
 #include "radix-tree.h"