diff --git a/tools/firmware-utils/src/mkwrggimg.c b/tools/firmware-utils/src/mkwrggimg.c
index a224b25b60..9995b9a13d 100644
--- a/tools/firmware-utils/src/mkwrggimg.c
+++ b/tools/firmware-utils/src/mkwrggimg.c
@@ -8,6 +8,7 @@
  *
  */
 
+#define _ANSI_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>