diff --git a/tools/mfkey/Makefile b/tools/mfkey/Makefile
index da7d431a..1744e35a 100755
--- a/tools/mfkey/Makefile
+++ b/tools/mfkey/Makefile
@@ -1,7 +1,7 @@
 VPATH = ../../common/crapto1 ../../client
 CC = gcc
 LD = gcc
-CFLAGS = -I../../common -I../../client -Wall -O4
+CFLAGS = -std=c99 -D_ISOC99_SOURCE -I../../common -I../../client -Wall -O3
 LDFLAGS =
 
 OBJS = crypto1.o crapto1.o util.o mfkey.o
diff --git a/tools/mfkey/mfkey64.c b/tools/mfkey/mfkey64.c
index 4e9876c5..1b002812 100755
--- a/tools/mfkey/mfkey64.c
+++ b/tools/mfkey/mfkey64.c
@@ -1,5 +1,5 @@
 #include <stdio.h>
-#include <strings.h>
+#include <string.h>
 #include <inttypes.h>
 #include "crapto1/crapto1.h"
 #include "util.h"