From a3df0523b5a4a114ac1615dc5f2c28d835e6fe18 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Tue, 5 Jan 2021 23:35:30 +0100
Subject: [PATCH] Fix crash when requesting disk/in monitoring of busses

e.g. select the master-bus, use  "D" or "I" keyboard shortcuts
in the mixer window.
---
 gtk2_ardour/mixer_ui.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gtk2_ardour/mixer_ui.cc b/gtk2_ardour/mixer_ui.cc
index 1b49d398fb..27c58023cd 100644
--- a/gtk2_ardour/mixer_ui.cc
+++ b/gtk2_ardour/mixer_ui.cc
@@ -3915,6 +3915,11 @@ Mixer_UI::toggle_monitor_action (MonitorChoice monitor_choice, bool group_overri
 	for (AxisViewSelection::iterator i = _selection.axes.begin(); i != _selection.axes.end(); ++i) {
 		boost::shared_ptr<ARDOUR::Route> rt = boost::dynamic_pointer_cast<ARDOUR::Route> ((*i)->stripable());
 
+		if (!rt->monitoring_control ()) {
+			/* skip busses */
+			continue;
+		}
+
 		if (rt->monitoring_control()->monitoring_choice() & monitor_choice) {
 			mc = MonitorChoice (rt->monitoring_control()->monitoring_choice() & ~monitor_choice);
 		} else {