diff --git a/demos/gtk-demo/main.c b/demos/gtk-demo/main.c
index 5af0da3cdc..9de99cd937 100644
--- a/demos/gtk-demo/main.c
+++ b/demos/gtk-demo/main.c
@@ -142,6 +142,9 @@ activate_run (GSimpleAction *action,
           cbdata->model = model;
           cbdata->path = gtk_tree_model_get_path (model, &iter);
 
+          gtk_window_set_transient_for (GTK_WINDOW (demo), GTK_WINDOW (window));
+          gtk_window_set_modal (GTK_WINDOW (demo), TRUE);
+
           g_signal_connect (demo, "destroy",
                             G_CALLBACK (window_closed_cb), cbdata);
         }