diff --git a/gtk2_ardour/io_plugin_window.cc b/gtk2_ardour/io_plugin_window.cc
index 36c4c28e59..d94ff2577b 100644
--- a/gtk2_ardour/io_plugin_window.cc
+++ b/gtk2_ardour/io_plugin_window.cc
@@ -335,7 +335,9 @@ IOPluginWindow::IOPlugUI::edit_plugin (bool custom_ui)
 	_window_proxy->set_custom_ui_mode (custom_ui);
 	_window_proxy->show_the_right_window ();
 	Gtk::Window* tlw = dynamic_cast<Gtk::Window*> (get_toplevel ());
-	_window_proxy->set_transient_for (*tlw);
+	if (tlw) {
+		_window_proxy->set_transient_for (*tlw);
+	}
 }
 
 bool
diff --git a/gtk2_ardour/port_insert_ui.cc b/gtk2_ardour/port_insert_ui.cc
index c524b4af39..99772003af 100644
--- a/gtk2_ardour/port_insert_ui.cc
+++ b/gtk2_ardour/port_insert_ui.cc
@@ -288,8 +288,10 @@ PortInsertUI::edit_latency_button_clicked ()
 		   different WM's as possible.
 		*/
 		_latency_dialog->set_keep_above (true);
-		_latency_dialog->set_transient_for (*_parent);
 		_latency_dialog->add (*_latency_gui);
+		if (_parent) {
+			_latency_dialog->set_transient_for (*_parent);
+		}
 	}
 
 	_latency_gui->refresh ();
diff --git a/gtk2_ardour/processor_box.cc b/gtk2_ardour/processor_box.cc
index 681c0fe3f3..8e63fc9549 100644
--- a/gtk2_ardour/processor_box.cc
+++ b/gtk2_ardour/processor_box.cc
@@ -4461,7 +4461,9 @@ ProcessorBox::edit_processor (std::shared_ptr<Processor> processor)
 		proxy->show_the_right_window ();
 
 		Gtk::Window* tlw = dynamic_cast<Gtk::Window*> (get_toplevel ());
-		proxy->set_transient_for (*tlw);
+		if (tlw) {
+			proxy->set_transient_for (*tlw);
+		}
 	}
 }
 
@@ -4485,7 +4487,9 @@ ProcessorBox::generic_edit_processor (std::shared_ptr<Processor> processor)
 		proxy->show_the_right_window ();
 
 		Gtk::Window* tlw = dynamic_cast<Gtk::Window*> (get_toplevel ());
-		proxy->set_transient_for (*tlw);
+		if (tlw) {
+			proxy->set_transient_for (*tlw);
+		}
 	}
 }
 
@@ -4500,8 +4504,9 @@ ProcessorBox::manage_pins (std::shared_ptr<Processor> processor)
 		proxy->get (true);
 
 		Gtk::Window* tlw = dynamic_cast<Gtk::Window*> (get_toplevel ());
-		assert (tlw);
-		proxy->set_transient_for (*tlw);
+		if (tlw) {
+			proxy->set_transient_for (*tlw);
+		}
 
 		proxy->present();
 	}
diff --git a/gtk2_ardour/trigger_clip_picker.cc b/gtk2_ardour/trigger_clip_picker.cc
index f7e232bd4e..926954e05d 100644
--- a/gtk2_ardour/trigger_clip_picker.cc
+++ b/gtk2_ardour/trigger_clip_picker.cc
@@ -693,7 +693,9 @@ TriggerClipPicker::open_dir ()
 	Gtk::Window* tlw = dynamic_cast<Gtk::Window*> (get_toplevel ());
 	assert (tlw);
 #ifndef __APPLE__
-	_fcd.set_transient_for (*tlw);
+	if (tlw) {
+		_fcd.set_transient_for (*tlw);
+	}
 #endif
 
 	int result = _fcd.run ();