diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 8c6e9c707f..b2cfaf320a 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -1539,7 +1539,7 @@ Session::auto_connect_surround_master ()
 
 	/* Mute non-surround path */
 	if (_monitor_out) {
-		_monitor_out->monitor_control ()->set_mono (true);
+		_monitor_out->monitor_control ()->set_cut_all (true);
 	} else if (_master_out) {
 		_master_out->mute_control ()->set_value (true, PBD::Controllable::NoGroup);
 	}