diff -up gnome-power-manager-2.31.6/src/gpm-brightness.c.backlight-is-None gnome-power-manager-2.31.6/src/gpm-brightness.c
--- gnome-power-manager-2.31.6/src/gpm-brightness.c.backlight-is-None	2010-08-15 19:57:12.636000106 -0400
+++ gnome-power-manager-2.31.6/src/gpm-brightness.c	2010-08-15 19:57:20.948000051 -0400
@@ -176,6 +176,9 @@ gpm_brightness_output_get_internal (GpmB
 
 	g_return_val_if_fail (GPM_IS_BRIGHTNESS (brightness), FALSE);
 
+	if (brightness->priv->backlight == None)
+		return FALSE;
+
 	if (XRRGetOutputProperty (brightness->priv->dpy, output, brightness->priv->backlight,
 				  0, 4, False, False, None,
 				  &actual_type, &actual_format,
