diff --git a/flash-tool/usb.c b/flash-tool/usb.c
index 15fa5f2..39711be 100644
--- a/flash-tool/usb.c
+++ b/flash-tool/usb.c
@@ -23,6 +23,7 @@
 #include "usb_boot_defines.h"
 #include <usb.h>
 #include <stdio.h>
+#include <string.h>
 
 extern unsigned int total_size;