diff --git a/modules/simpletest/tests/actions_loop_test.module b/modules/simpletest/tests/actions_loop_test.module
index 261cb80..ad3cad7 100644
--- a/modules/simpletest/tests/actions_loop_test.module
+++ b/modules/simpletest/tests/actions_loop_test.module
@@ -83,7 +83,7 @@ function watchdog_skip_semaphore($type, $message, $variables = array(), $severit
     'user'        => $user,
     'uid'         => isset($user->uid) ? $user->uid : 0,
     'request_uri' => $base_root . request_uri(),
-    'referer'     => $_SERVER['HTTP_REFERER'],
+    'referer'     => isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : '',
     'ip'          => ip_address(),
     'timestamp'   => REQUEST_TIME,
   );