diff --git a/builtin/commit.c b/builtin/commit.c
index 7da5f92..5373199 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -340,7 +340,7 @@ static void create_base_index(const struct commit *current_head)
 	if (!tree)
 		die(_("failed to unpack HEAD tree object"));
 	parse_tree(tree);
-	init_tree_desc(&t, tree->buffer, tree->size);
+	init_tree_desc(&t, &tree->object.oid, tree->buffer, tree->size);
 	if (unpack_trees(1, &t, &opts))
 		exit(128); /* We've already reported the error, finish dying */
 }