diff --git a/core/lib/Drupal/Component/Serialization/YamlSymfony.php b/core/lib/Drupal/Component/Serialization/YamlSymfony.php
index d35e09cd48..efe3039df7 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);
+      return $yaml->parse($raw, SymfonyYaml::PARSE_EXCEPTION_ON_INVALID_TYPE | SymfonyYaml::PARSE_KEYS_AS_STRINGS);
     }
     catch (\Exception $e) {
       throw new InvalidDataTypeException($e->getMessage(), $e->getCode(), $e);
diff --git a/core/tests/Drupal/Tests/Core/StackMiddleware/ReverseProxyMiddlewareTest.php b/core/tests/Drupal/Tests/Core/StackMiddleware/ReverseProxyMiddlewareTest.php
index b7a784d487..c42ff5c028 100644
--- a/core/tests/Drupal/Tests/Core/StackMiddleware/ReverseProxyMiddlewareTest.php
+++ b/core/tests/Drupal/Tests/Core/StackMiddleware/ReverseProxyMiddlewareTest.php
@@ -47,6 +47,10 @@ public function testNoProxy() {
    * Tests that subscriber sets trusted headers when reverse proxy is set.
    *
    * @dataProvider reverseProxyEnabledProvider
+   *
+   * @group legacy
+   *
+   * @expectedDeprecation The "Symfony\Component\HttpFoundation\Request::setTrustedHeaderName()" method is deprecated since version 3.3 and will be removed in 4.0. Use the $trustedHeaderSet argument of the Request::setTrustedProxies() method instead.
    */
   public function testReverseProxyEnabled($provided_settings) {
     // Enable reverse proxy and add test values.
@@ -87,10 +91,10 @@ protected function trustedHeadersAreSet(Settings $settings) {
     $request = new Request();
 
     $middleware->handle($request);
-    $this->assertSame($settings->get('reverse_proxy_header'), $request->getTrustedHeaderName($request::HEADER_CLIENT_IP));
-    $this->assertSame($settings->get('reverse_proxy_proto_header'), $request->getTrustedHeaderName($request::HEADER_CLIENT_PROTO));
-    $this->assertSame($settings->get('reverse_proxy_host_header'), $request->getTrustedHeaderName($request::HEADER_CLIENT_HOST));
-    $this->assertSame($settings->get('reverse_proxy_port_header'), $request->getTrustedHeaderName($request::HEADER_CLIENT_PORT));
+    $this->assertSame($settings->get('reverse_proxy_header'), $request->getTrustedHeaderName($request::HEADER_X_FORWARDED_FOR));
+    $this->assertSame($settings->get('reverse_proxy_proto_header'), $request->getTrustedHeaderName($request::HEADER_X_FORWARDED_PROTO));
+    $this->assertSame($settings->get('reverse_proxy_host_header'), $request->getTrustedHeaderName($request::HEADER_X_FORWARDED_HOST));
+    $this->assertSame($settings->get('reverse_proxy_port_header'), $request->getTrustedHeaderName($request::HEADER_X_FORWARDED_PORT));
     $this->assertSame($settings->get('reverse_proxy_forwarded_header'), $request->getTrustedHeaderName($request::HEADER_FORWARDED));
     $this->assertSame($settings->get('reverse_proxy_addresses'), $request->getTrustedProxies());
   }