diff --git a/gtk/gtktogglebutton.h b/gtk/gtktogglebutton.h
index 5f71653873..f9ca07e41b 100644
--- a/gtk/gtktogglebutton.h
+++ b/gtk/gtktogglebutton.h
@@ -52,9 +52,9 @@ struct _GtkToggleButton
 {
   GtkButton button;
 
-  guint active : 1;
-  guint draw_indicator : 1;
-  guint inconsistent : 1;
+  guint GSEAL (active : 1);
+  guint GSEAL (draw_indicator : 1);
+  guint GSEAL (inconsistent : 1);
 };
 
 struct _GtkToggleButtonClass