--- xorg-server-1.5.1/hw/xfree86/modes/xf86Crtc.c.bak	2008-11-04 21:05:49.000000000 +0100
+++ xorg-server-1.5.1/hw/xfree86/modes/xf86Crtc.c	2008-11-04 21:04:43.000000000 +0100
@@ -1176,10 +1176,12 @@ xf86InitialOutputPositions (ScrnInfoPtr
 			output->initial_x += xf86ModeWidth (modes[or], relative->initial_rotation);
 		    break;
 		case OPTION_ABOVE:
-		    output->initial_y -= xf86ModeHeight (modes[o], relative->initial_rotation);
+		    if (modes[o])
+			output->initial_y -= xf86ModeHeight (modes[o], relative->initial_rotation);
 		    break;
 		case OPTION_LEFT_OF:
-		    output->initial_x -= xf86ModeWidth (modes[o], relative->initial_rotation);
+		    if (modes[o])
+			output->initial_x -= xf86ModeWidth (modes[o], relative->initial_rotation);
 		    break;
 		default:
 		    break;