diff --git a/gtk2_ardour/plugin_display.h b/gtk2_ardour/plugin_display.h
index 4a2587e79f..2573af2578 100644
--- a/gtk2_ardour/plugin_display.h
+++ b/gtk2_ardour/plugin_display.h
@@ -40,7 +40,7 @@ protected:
 		_qdraw_connection.disconnect ();
 	}
 
-	void update_height_alloc (uint32_t inline_height);
+	virtual void update_height_alloc (uint32_t inline_height);
 	virtual uint32_t render_inline (cairo_t *, uint32_t width);
 
 	virtual void display_frame (cairo_t* cr, double w, double h);