diff --git a/libs/canvas/canvas.cc b/libs/canvas/canvas.cc
index 9e47792758..1995608a9f 100644
--- a/libs/canvas/canvas.cc
+++ b/libs/canvas/canvas.cc
@@ -401,7 +401,13 @@ GtkCanvas::GtkCanvas ()
 	add_events (Gdk::BUTTON_PRESS_MASK | Gdk::BUTTON_RELEASE_MASK | Gdk::POINTER_MOTION_MASK |
 		    Gdk::SCROLL_MASK | Gdk::ENTER_NOTIFY_MASK | Gdk::LEAVE_NOTIFY_MASK |
 		    Gdk::KEY_PRESS_MASK | Gdk::KEY_RELEASE_MASK);
+}
 
+void
+GtkCanvas::use_nsglview ()
+{
+	assert (!_nsglview);
+	assert (!is_realized());
 #ifdef ARDOUR_CANVAS_NSVIEW_TAG // patched gdkquartz.h
 # ifndef __ppc__ // would need to flip RGBA <> RGBA
 	_nsglview = Gtkmm2ext::nsglview_create (this);
diff --git a/libs/canvas/canvas/canvas.h b/libs/canvas/canvas/canvas.h
index 60e75bf8bf..ec66f71025 100644
--- a/libs/canvas/canvas/canvas.h
+++ b/libs/canvas/canvas/canvas.h
@@ -181,6 +181,8 @@ public:
 	GtkCanvas ();
 	~GtkCanvas () { _in_dtor = true ; }
 
+	void use_nsglview ();
+
 	void request_redraw (Rect const &);
 	void request_size (Duple);
 	void grab (Item *);