diff --git a/refs/files-backend.c b/refs/files-backend.c
index b899543..6f257c7 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -1,5 +1,6 @@
 #include "../cache.h"
 #include "../config.h"
+#include "../hex.h"
 #include "../refs.h"
 #include "refs-internal.h"
 #include "ref-cache.h"