diff --git a/gtk/gtkexpander.h b/gtk/gtkexpander.h
index 97163dc5c1..dc07a6ce71 100644
--- a/gtk/gtkexpander.h
+++ b/gtk/gtkexpander.h
@@ -47,7 +47,7 @@ struct _GtkExpander
 {
   GtkBin              bin;
 
-  GtkExpanderPrivate *priv;
+  GtkExpanderPrivate *GSEAL (priv);
 };
 
 struct _GtkExpanderClass