diff --git a/gtk/gtkcombobox.h b/gtk/gtkcombobox.h
index 8f5e1456e1..cc93415a0c 100644
--- a/gtk/gtkcombobox.h
+++ b/gtk/gtkcombobox.h
@@ -46,7 +46,7 @@ struct _GtkComboBox
   GtkBin parent_instance;
 
   /*< private >*/
-  GtkComboBoxPrivate *priv;
+  GtkComboBoxPrivate *GSEAL (priv);
 };
 
 struct _GtkComboBoxClass