diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index b02dc5a7e3..d7d344de73 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -242,6 +242,7 @@ struct ref_transaction {
 	size_t alloc;
 	size_t nr;
 	enum ref_transaction_state state;
+	void *backend_data;
 };
 
 /*