diff --git a/hash_lib.h b/hash_lib.h
index 27d9aeb..dfffb77 100644
--- a/hash_lib.h
+++ b/hash_lib.h
@@ -5,6 +5,7 @@
 #ifdef __cplusplus
 #include <string>
 #include <vector>
+#include <string.h>
 #include "fileop.h"
 namespace hash_lib {
     class Hash {