diff --git a/gtk2_ardour/public_editor.h b/gtk2_ardour/public_editor.h
index 184cb77d52..ff77387ce1 100644
--- a/gtk2_ardour/public_editor.h
+++ b/gtk2_ardour/public_editor.h
@@ -271,8 +271,10 @@ class PublicEditor : public Gtk::Window, public PBD::StatefulDestructible, publi
 	virtual framecnt_t current_page_samples() const = 0;
 	virtual double visible_canvas_height () const = 0;
 	virtual void temporal_zoom_step (bool coarser) = 0;
-        virtual void ensure_time_axis_view_is_visible (const TimeAxisView& tav, bool at_top = false) { 
-	    _ensure_time_axis_view_is_visible (tav, at_top);
+	/* The virtual version, without a default argument, is protected below.
+	 */
+        void ensure_time_axis_view_is_visible (TimeAxisView const & tav, bool at_top = false) { 
+		_ensure_time_axis_view_is_visible (tav, at_top);
 	}
         virtual void override_visible_track_count () = 0;
 	virtual void scroll_tracks_down_line () = 0;
@@ -420,7 +422,12 @@ class PublicEditor : public Gtk::Window, public PBD::StatefulDestructible, publi
 	PBD::Signal0<void> MouseModeChanged;
 
   protected:
-       virtual void _ensure_time_axis_view_is_visible (const TimeAxisView& tav, bool at_top) = 0;
+	/* This _ variant of ensure_time_axis_view_is_visible exists because
+	   C++ doesn't really like default values for virtual methods. So the
+	   public version is non-virtual, with a default value; the virtual
+	   (and protected) method here does not have a default value.
+	*/
+       virtual void _ensure_time_axis_view_is_visible (TimeAxisView const & tav, bool at_top) = 0;
 };
 
 #endif // __gtk_ardour_public_editor_h__