diff --git a/tree.c b/tree.c
index f416afc..0ebb8c5 100644
--- a/tree.c
+++ b/tree.c
@@ -197,7 +197,7 @@ int read_tree(struct repository *r, struct tree *tree, int stage,
 
 struct tree *lookup_tree(struct repository *r, const struct object_id *oid)
 {
-	struct object *obj = lookup_object(r, oid->hash);
+	struct object *obj = lookup_object(r, oid);
 	if (!obj)
 		return create_object(r, oid->hash,
 				     alloc_tree_node(r));