diff --git a/util/cbfstool/flashmap/fmap.c b/util/cbfstool/flashmap/fmap.c
index 5438d49f8f..f143beb90f 100644
--- a/util/cbfstool/flashmap/fmap.c
+++ b/util/cbfstool/flashmap/fmap.c
@@ -32,6 +32,8 @@
  * Software Foundation.
  */
 
+#define _XOPEN_SOURCE 700
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>