diff --git a/gtk2_ardour/ardour_ui.cc b/gtk2_ardour/ardour_ui.cc
index f58c36f69a..9a255d24d8 100644
--- a/gtk2_ardour/ardour_ui.cc
+++ b/gtk2_ardour/ardour_ui.cc
@@ -387,6 +387,7 @@ ARDOUR_UI::ARDOUR_UI (int *argcp, char **argvp[], const char* localedir)
 	WM::Manager::instance().register_window (&midi_port_matrix);
 
     session_lock_dialog->set_deletable (false);
+	session_lock_dialog->set_modal (true); 
     
 	/* We need to instantiate the theme manager because it loads our
 	   theme files. This should really change so that its window