diff --git a/package/system/mtd/src/mtd.c b/package/system/mtd/src/mtd.c
index 7b80193b44c..6dd6eea6a36 100644
--- a/package/system/mtd/src/mtd.c
+++ b/package/system/mtd/src/mtd.c
@@ -21,6 +21,7 @@
  * The code is based on the linux-mtd examples.
  */
 
+#define _GNU_SOURCE
 #include <limits.h>
 #include <unistd.h>
 #include <stdlib.h>