diff --git a/modules/update/update.fetch.inc b/modules/update/update.fetch.inc
index bf0039f..9e04bcb 100644
--- a/modules/update/update.fetch.inc
+++ b/modules/update/update.fetch.inc
@@ -156,7 +156,8 @@ function _update_process_fetch_task($project) {
     }
   }
 
-  if (!empty($data)) {
+  $data = '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"><html><head></head><body></body></html>';
+  if ((!empty($data)) && (preg_match('/\A<\?xml/simx', $data))) {
     $available = update_parse_xml($data);
     // @todo: Purge release data we don't need (http://drupal.org/node/238950).
     if (!empty($available)) {
