diff --git a/gtk/gtktreesortable.c b/gtk/gtktreesortable.c
index 75f7e3c66e..111a3e53ac 100644
--- a/gtk/gtktreesortable.c
+++ b/gtk/gtktreesortable.c
@@ -111,8 +111,8 @@ gtk_tree_sortable_sort_column_changed (GtkTreeSortable *sortable)
 /**
  * gtk_tree_sortable_get_sort_column_id:
  * @sortable: A #GtkTreeSortable
- * @sort_column_id: The sort column id to be filled in
- * @order: The #GtkSortType to be filled in
+ * @sort_column_id: (out): The sort column id to be filled in
+ * @order: (out): The #GtkSortType to be filled in
  * 
  * Fills in @sort_column_id and @order with the current sort column and the
  * order. It returns %TRUE unless the @sort_column_id is