--- modules/gravatar/gravatar.module.original	2008-11-08 22:22:20.000000000 +0100
+++ modules/gravatar/gravatar.module	2008-11-14 21:03:24.546875000 +0100
@@ -276,7 +276,10 @@ function _gravatar_get_gravatar($email) 
       // drupal default picture
       case 1:
         $path = variable_get('user_picture_default', '');
-        //$path = url($path, array('absolute' => TRUE)); // fixe URL with absolute path ?
+        // prepend base url to relative paths
+        if(!valid_url($path,TRUE)) {
+          $path = $base_url . '/' . $path;
+        }
         $gravatar .= '?d=' . urlencode($path);
         break;
       // gravatar module default picture