--- includes/common.inc.orig	2006-12-13 19:57:32.034238416 -0500
+++ includes/common.inc	2006-12-13 19:58:44.562212488 -0500
@@ -1426,7 +1426,8 @@
   }
 
   $preprocess_css = variable_get('preprocess_css', FALSE);
-  $directory = file_directory_path();
+  // when called from drupal_bootstrap_database file.inc hasn't been included yet.
+  $directory = function_exists('file_directory_path') ? file_directory_path() : FALSE;
   $is_writable = is_dir($directory) && is_writable($directory) && (variable_get('file_downloads', FILE_DOWNLOADS_PUBLIC) == FILE_DOWNLOADS_PUBLIC);
 
   foreach ($css as $media => $types) {