diff --git a/gtk/gtkmenu.c b/gtk/gtkmenu.c
index 2f04718b16..bbbe4c0727 100644
--- a/gtk/gtkmenu.c
+++ b/gtk/gtkmenu.c
@@ -1400,7 +1400,7 @@ popup_grab_on_window (GdkWindow *window,
  * @parent_menu_shell: (allow-none): the menu shell containing the triggering menu item, or %NULL
  * @parent_menu_item: (allow-none): the menu item whose activation triggered the popup, or %NULL
  * @func: (allow-none): a user supplied function used to position the menu, or %NULL
- * @data: user supplied data to be passed to @func.
+ * @data: (allow-none): user supplied data to be passed to @func.
  * @button: the mouse button which was pressed to initiate the event.
  * @activate_time: the time at which the activation event occurred.
  *