diff --git a/demos/gtk-demo/colorsel.c b/demos/gtk-demo/colorsel.c
index 73042f932f..566af21e52 100644
--- a/demos/gtk-demo/colorsel.c
+++ b/demos/gtk-demo/colorsel.c
@@ -52,6 +52,7 @@ change_color_callback (GtkWidget *button,
   GtkWidget *dialog;
 
   dialog = gtk_color_chooser_dialog_new ("Changing color", GTK_WINDOW (window));
+  gtk_window_set_modal (GTK_WINDOW (dialog), TRUE);
   gtk_color_chooser_set_rgba (GTK_COLOR_CHOOSER (dialog), &color);
 
   g_signal_connect (dialog,