diff --git a/gtk2_ardour/editor_canvas_events.cc b/gtk2_ardour/editor_canvas_events.cc
index b6129af5e9..b65af5ac09 100644
--- a/gtk2_ardour/editor_canvas_events.cc
+++ b/gtk2_ardour/editor_canvas_events.cc
@@ -1293,10 +1293,13 @@ Editor::canvas_grid_zone_event (GdkEvent* event)
 	GdkEventScroll scroll;
 	ArdourCanvas::Duple winpos;
 
+
 	switch (event->type) {
 
 		case GDK_BUTTON_PRESS:
-			choose_mapping_drag (_canvas_grid_zone, event);
+			if (event->button.button == 1) {
+				choose_mapping_drag (_canvas_grid_zone, event);
+			}
 			break;
 
 		case GDK_BUTTON_RELEASE: