diff --git a/gtk/gtklistbox.h b/gtk/gtklistbox.h
index 0e41498bda..68f02549f6 100644
--- a/gtk/gtklistbox.h
+++ b/gtk/gtklistbox.h
@@ -121,6 +121,9 @@ typedef void (*GtkListBoxUpdateHeaderFunc) (GtkListBoxRow *row,
  * Called for list boxes that are bound to a `GListModel` with
  * gtk_list_box_bind_model() for each item that gets added to the model.
  *
+ * If the widget returned is not a #GtkListBoxRow widget, then the widget
+ * will be inserted as the child of an intermediate #GtkListBoxRow.
+ *
  * Returns: (transfer full): a `GtkWidget` that represents @item
  */
 typedef GtkWidget * (*GtkListBoxCreateWidgetFunc) (gpointer item,