--- includes/common.inc	2010-10-27 01:17:50.000000000 +1000
+++ includes/commonNew.inc	2010-10-27 12:52:55.905423801 +1000
@@ -2805,8 +2805,8 @@ function drupal_add_css($data = NULL, $o
       '!IE' => TRUE,
     );
 
-    // Files with a query string cannot be preprocessed.
-    if ($options['type'] === 'file' && $options['preprocess'] && strpos($options['data'], '?') !== FALSE) {
+    // Files with a query string or external files cannot be preprocessed.
+     if ($options['type'] === 'file' && ($options['preprocess'] && strpos($options['data'], '?') !== FALSE) || url_is_external($data)) {
       $options['preprocess'] = FALSE;
     }