diff -up gnome-session-3.0.1/tools/gnome-session-check-accelerated-helper.c.jx gnome-session-3.0.1/tools/gnome-session-check-accelerated-helper.c
--- gnome-session-3.0.1/tools/gnome-session-check-accelerated-helper.c.jx	2011-06-03 13:29:43.000000000 -0400
+++ gnome-session-3.0.1/tools/gnome-session-check-accelerated-helper.c	2011-06-03 13:31:22.000000000 -0400
@@ -278,6 +278,11 @@ main (int argc, char **argv)
                 goto out;
         }
 
+	if (ScreenCount(display) > 1) {
+		_print_error ("Zaphod mode not supported.");
+		goto out;
+	}
+
         if (_has_composite (display) != 0) {
                 _print_error ("No composite extension.");
                 goto out;
