diff --git a/gtk2_ardour/transport_masters_dialog.cc b/gtk2_ardour/transport_masters_dialog.cc
index dc0d4da206..cd00d56460 100644
--- a/gtk2_ardour/transport_masters_dialog.cc
+++ b/gtk2_ardour/transport_masters_dialog.cc
@@ -287,9 +287,10 @@ TransportMastersWidget::update_ports ()
 	}
 
 	for (vector<Row*>::iterator r = rows.begin(); r != rows.end(); ++r) {
-		(*r)->port_choice_changed ();
+		if ((*r)->tm->port()) {
+			(*r)->build_port_list ((*r)->tm->port()->type());
+		}
 	}
-
 }
 
 void
@@ -531,8 +532,6 @@ TransportMastersWidget::Row::port_choice_changed ()
 		return;
 	}
 
-	build_port_list (tm->port()->type());
-
 	TreeModel::iterator active = port_combo.get_active ();
 	string new_port = (*active)[parent.port_columns.full_name];