diff --git a/core/modules/system/src/Tests/System/DateFormatsMachineNameTest.php b/core/modules/system/src/Tests/System/DateFormatsMachineNameTest.php
index a273515..f06f3f7 100644
--- a/core/modules/system/src/Tests/System/DateFormatsMachineNameTest.php
+++ b/core/modules/system/src/Tests/System/DateFormatsMachineNameTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\system\Tests\System;
 
-use Drupal\Component\Utility\Unicode;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -61,7 +60,7 @@ public function testDateFormatsMachineNameAllowedValues() {
     $this->assertText(t('The machine-readable name is already in use. It must be unique.'), 'It is not possible to create a date format with the machine name "fallback". It is a built-in format that already exists.');
 
     // Create a date format with a machine name distinct from the previous two.
-    $id = Unicode::strtolower($this->randomMachineName(16));
+    $id = $this->randomLowercaseMachineName(16);
     $edit = array(
       'label' => $this->randomMachineName(16),
       'id' => $id,