diff --git a/hmac.h b/hmac.h
index dcba105..6344392 100644
--- a/hmac.h
+++ b/hmac.h
@@ -4,6 +4,7 @@
 #ifndef HMAC_H
 #define HMAC_H
 
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>