diff --git a/core/modules/system/src/Tests/Common/UrlTest.php b/core/modules/system/src/Tests/Common/UrlTest.php
index 3c43406..f52d022 100644
--- a/core/modules/system/src/Tests/Common/UrlTest.php
+++ b/core/modules/system/src/Tests/Common/UrlTest.php
@@ -313,12 +313,12 @@ function testExternalUrls() {
     $url = $test_url;
     $query = array($this->randomMachineName(5) => $this->randomMachineName(5));
     $result = Url::fromUri($url, array('query' => $query))->toString();
-    $this->assertEqual($url . '?' . UrlHelper::buildQuery($query), $result, 'External URL can be extended with a query string in $options.');
+    $this->assertEqual($url . '?' . http_build_query($query, '', '&'), $result, 'External URL can be extended with a query string in $options.');
 
     // Verify query string can be extended in an external URL.
     $url = $test_url . '?drupal=awesome';
     $query = array($this->randomMachineName(5) => $this->randomMachineName(5));
     $result = Url::fromUri($url, array('query' => $query))->toString();
-    $this->assertEqual($url . '&' . UrlHelper::buildQuery($query), $result);
+    $this->assertEqual($url . '&' . http_build_query($query, '', '&'), $result);
   }
 }