diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 05195e0..0e104e4 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -2085,6 +2085,10 @@ protected function buildXPathQuery($xpath, array $args = array()) {
    *
    * @param $xpath
    *   The xpath string to use in the search.
+   * @param $arguments
+   *   An array of arguments with keys in the form ':name' matching the
+   *   placeholders in the query. The values may be either strings or numeric
+   *   values.
    *
    * @return
    *   The return value of the xpath search. For details on the xpath string