diff --git a/core/lib/Drupal/Component/Serialization/YamlSymfony.php b/core/lib/Drupal/Component/Serialization/YamlSymfony.php
index efe3039df76497af4bbe5e634047b8059ccc2e93..d35e09cd4821923b63cf2dbe116bbf16ab7cb452 100644
--- a/core/lib/Drupal/Component/Serialization/YamlSymfony.php
+++ b/core/lib/Drupal/Component/Serialization/YamlSymfony.php
@@ -34,7 +34,7 @@ public static function decode($raw) {
       $yaml = new Parser();
       // Make sure we have a single trailing newline. A very simple config like
       // 'foo: bar' with no newline will fail to parse otherwise.
-      return $yaml->parse($raw, SymfonyYaml::PARSE_EXCEPTION_ON_INVALID_TYPE | SymfonyYaml::PARSE_KEYS_AS_STRINGS);
+      return $yaml->parse($raw, SymfonyYaml::PARSE_EXCEPTION_ON_INVALID_TYPE);
     }
     catch (\Exception $e) {
       throw new InvalidDataTypeException($e->getMessage(), $e->getCode(), $e);
diff --git a/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php b/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
index 797a17362ae5ad4a51a9503132830e3c1a5adfd6..08c84a19c65e896586f9cec751f8a4054b2b6912 100644
--- a/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
+++ b/core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php
@@ -185,7 +185,6 @@ public static function getSkippedDeprecations() {
       'The Symfony\Component\HttpFoundation\Session\Storage\Handler\WriteCheckSessionHandler class is deprecated since Symfony 3.4 and will be removed in 4.0. Implement `SessionUpdateTimestampHandlerInterface` or extend `AbstractSessionHandler` instead.',
       'The "session_handler.write_check" service relies on the deprecated "Symfony\Component\HttpFoundation\Session\Storage\Handler\WriteCheckSessionHandler" class. It should either be deprecated or its implementation upgraded.',
       'Not setting the strict option of the Choice constraint to true is deprecated since Symfony 3.4 and will throw an exception in 4.0.',
-      'Using the Yaml::PARSE_KEYS_AS_STRINGS flag is deprecated since Symfony 3.4 as it will be removed in 4.0. Quote your keys when they are evaluable instead.',
       'Drupal\node\Plugin\Action\DeleteNode is deprecated in Drupal 8.6.x, will be removed before Drupal 9.0.0. Use \Drupal\Core\Action\Plugin\Action\DeleteAction instead. See https://www.drupal.org/node/2934349.',
       'Drupal\comment\Plugin\Action\DeleteComment is deprecated in Drupal 8.6.x, will be removed before Drupal 9.0.0. Use \Drupal\Core\Action\Plugin\Action\DeleteAction instead. See https://www.drupal.org/node/2934349.',
     ];