core/modules/system/tests/src/Functional/Common/UrlTest.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/modules/system/tests/src/Functional/Common/UrlTest.php b/core/modules/system/tests/src/Functional/Common/UrlTest.php
index cd27ca7..163be42 100644
--- a/core/modules/system/tests/src/Functional/Common/UrlTest.php
+++ b/core/modules/system/tests/src/Functional/Common/UrlTest.php
@@ -312,7 +312,7 @@ public function testExternalUrls() {
 
     // Verify query string can be extended in an external URL.
     $url = $test_url . '?drupal=awesome';
-    $query = [$this->randomMachineName(5) => $this->randomMachineName(5)];
+    $query = ['z' . $this->randomMachineName(5) => $this->randomMachineName(5)];
     $result = Url::fromUri($url, ['query' => $query])->toString();
     $this->assertEqual($url . '&' . http_build_query($query, '', '&'), $result);
   }