diff --git a/tools/mfkey/mfkey64.c b/tools/mfkey/mfkey64.c
index 45f0ffee2..dbf0bea9f 100644
--- a/tools/mfkey/mfkey64.c
+++ b/tools/mfkey/mfkey64.c
@@ -2,6 +2,7 @@
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <string.h>
 #include <stdlib.h>
 #include "crapto1/crapto1.h"
 #include "util_posix.h"