diff --git a/gtk2_ardour/generic_pluginui.cc b/gtk2_ardour/generic_pluginui.cc
index 979cd4405a..6fe5e8b7fd 100644
--- a/gtk2_ardour/generic_pluginui.cc
+++ b/gtk2_ardour/generic_pluginui.cc
@@ -231,18 +231,18 @@ GenericPluginUI::scroller_size_request (Gtk::Requisition* a)
 		screen = get_screen();
 	}
 
-	int maximum_width = -1;
-
-	if (screen) {
-		Gdk::Rectangle monitor;
-		const int monitor_num = screen->get_monitor_at_window (get_window ());
-		screen->get_monitor_geometry (
-				(monitor_num < 0) ? 0 : monitor_num,
-				monitor);
-
-		maximum_width = monitor.get_width() * 0.9;
+	if (!screen) {
+		return;
 	}
 
+	Gdk::Rectangle monitor;
+	const int monitor_num = screen->get_monitor_at_window (window);
+	screen->get_monitor_geometry (
+			(monitor_num < 0) ? 0 : monitor_num,
+			monitor);
+
+	const int maximum_width = monitor.get_width() * 0.9;
+
 	GtkRequisition request = hpacker.size_request();
 
 	if (request.width > maximum_width) {