diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index 4d0a8f2..0131508 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -11,6 +11,7 @@
 use Behat\Mink\Element\Element;
 use Behat\Mink\Mink;
 use Behat\Mink\Session;
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Cache\Cache;
@@ -876,15 +877,14 @@ public function installDrupal() {
     copy($settings_services_file, $directory . '/services.yml');
     if ($this->strictConfigSchema) {
       // Add a listener to validate configuration schema on save.
-      $yaml = new \Symfony\Component\Yaml\Yaml();
       $content = file_get_contents($directory . '/services.yml');
-      $services = $yaml->parse($content);
+      $services = Yaml::decode($content);
       $services['services']['simpletest.config_schema_checker'] = [
         'class' => 'Drupal\Core\Config\Testing\ConfigSchemaChecker',
         'arguments' => ['@config.typed'],
         'tags' => [['name' => 'event_subscriber']]
       ];
-      file_put_contents($directory . '/services.yml', $yaml->dump($services));
+      file_put_contents($directory . '/services.yml', Yaml::encode($services));
     }
 
     // Since Drupal is bootstrapped already, install_begin_request() will not