diff --git a/apply.h b/apply.h
index a795193435..da3d95fa50 100644
--- a/apply.h
+++ b/apply.h
@@ -1,6 +1,7 @@
 #ifndef APPLY_H
 #define APPLY_H
 
+#include "hash.h"
 #include "lockfile.h"
 #include "string-list.h"