diff --git a/composer.lock b/composer.lock
index dc13a581370aa75d4a49d529454bf130737be031..1d46b257095997657a45eb4a8875b138e564037b 100644
--- a/composer.lock
+++ b/composer.lock
@@ -528,7 +528,7 @@
             "dist": {
                 "type": "path",
                 "url": "core",
-                "reference": "02fb64caa7f852779c5ba9b94d7b48755612d45d"
+                "reference": "365584bd91d9f305a9bf0db5a9acecf55c22ba57"
             },
             "require": {
                 "asm89/stack-cors": "^1.1",
@@ -751,6 +751,7 @@
                     "lib/Drupal/Core/DependencyInjection/Container.php",
                     "lib/Drupal/Core/DrupalKernel.php",
                     "lib/Drupal/Core/DrupalKernelInterface.php",
+                    "lib/Drupal/Core/Http/InputBag.php",
                     "lib/Drupal/Core/Installer/InstallerRedirectTrait.php",
                     "lib/Drupal/Core/Site/Settings.php"
                 ],
@@ -7811,12 +7812,12 @@
             "version": "1.9.1",
             "source": {
                 "type": "git",
-                "url": "https://github.com/webmozart/assert.git",
+                "url": "https://github.com/webmozarts/assert.git",
                 "reference": "bafc69caeb4d49c39fd0779086c03a3738cbb389"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/webmozart/assert/zipball/bafc69caeb4d49c39fd0779086c03a3738cbb389",
+                "url": "https://api.github.com/repos/webmozarts/assert/zipball/bafc69caeb4d49c39fd0779086c03a3738cbb389",
                 "reference": "bafc69caeb4d49c39fd0779086c03a3738cbb389",
                 "shasum": ""
             },
@@ -7854,8 +7855,8 @@
                 "validate"
             ],
             "support": {
-                "issues": "https://github.com/webmozart/assert/issues",
-                "source": "https://github.com/webmozart/assert/tree/master"
+                "issues": "https://github.com/webmozarts/assert/issues",
+                "source": "https://github.com/webmozarts/assert/tree/1.9.1"
             },
             "time": "2020-07-08T17:02:28+00:00"
         }
diff --git a/core/composer.json b/core/composer.json
index 79019a8cf65dbc7e097dbbc8822a8b26a9559099..1b185cbe0f287ec8463356ceee15e0cf03219f0b 100644
--- a/core/composer.json
+++ b/core/composer.json
@@ -196,6 +196,7 @@
             "lib/Drupal/Core/DependencyInjection/Container.php",
             "lib/Drupal/Core/DrupalKernel.php",
             "lib/Drupal/Core/DrupalKernelInterface.php",
+            "lib/Drupal/Core/Http/InputBag.php",
             "lib/Drupal/Core/Installer/InstallerRedirectTrait.php",
             "lib/Drupal/Core/Site/Settings.php"
         ],
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index ee3b56e7bc391e4a787831a207fb60bab65bd522..599e13833ad94296ae9e9ea3f5dbdb96c2a1aeac 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -17,6 +17,7 @@
 use Drupal\Core\DependencyInjection\YamlFileLoader;
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\File\MimeType\MimeTypeGuesser;
+use Drupal\Core\Http\InputBag;
 use Drupal\Core\Http\TrustedHostsRequestFactory;
 use Drupal\Core\Installer\InstallerKernel;
 use Drupal\Core\Installer\InstallerRedirectTrait;
@@ -33,6 +34,7 @@
 use Symfony\Component\HttpKernel\Exception\BadRequestHttpException;
 use Symfony\Component\HttpKernel\Exception\HttpExceptionInterface;
 use Symfony\Component\HttpKernel\TerminableInterface;
+use Symfony\Component\HttpFoundation\InputBag as SymfonyInputBag;
 use TYPO3\PharStreamWrapper\Manager as PharStreamWrapperManager;
 use TYPO3\PharStreamWrapper\Behavior as PharStreamWrapperBehavior;
 use TYPO3\PharStreamWrapper\PharStreamWrapper;
@@ -692,6 +694,14 @@ public function handle(Request $request, $type = self::MASTER_REQUEST, $catch =
     // Ensure sane PHP environment variables.
     static::bootEnvironment();
 
+    // Replace ParameterBag with InputBag for compatibility with Symfony 5.
+    // @todo Remove this when Symfony 4 is no longer supported.
+    foreach (['request', 'query', 'cookies'] as $bag) {
+      if (!($bag instanceof SymfonyInputBag)) {
+        $request->$bag = new InputBag($request->$bag->all());
+      }
+    }
+
     try {
       $this->initializeSettings($request);
 
diff --git a/core/lib/Drupal/Core/Http/InputBag.php b/core/lib/Drupal/Core/Http/InputBag.php
new file mode 100644
index 0000000000000000000000000000000000000000..b4409cced4f016551dd9438d06765cf146f90af9
--- /dev/null
+++ b/core/lib/Drupal/Core/Http/InputBag.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Drupal\Core\Http;
+
+use Symfony\Component\HttpFoundation\ParameterBag;
+
+/**
+ * Forward compatibility class for Symfony 5.
+ *
+ * @internal only used as a bridge from Symfony 4 to Symfony 5, will be removed
+ *   in drupal:10.0.0.
+ */
+final class InputBag extends ParameterBag {
+
+  /**
+   * Returns the parameters.
+   *
+   * @param string|null $key
+   *   The name of the parameter to return or null to get them all.
+   *
+   * @return array
+   *   An array of parameters.
+   */
+  public function all(string $key = NULL): array {
+    if ($key === NULL) {
+      return $this->parameters;
+    }
+
+    $value = $this->parameters[$key] ?? [];
+    if (!is_array($value)) {
+      throw new \UnexpectedValueException(sprintf('Unexpected value for parameter "%s": expecting "array", got "%s".', $key, get_debug_type($value)));
+    }
+
+    return $value;
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Core/Http/InputBagTest.php b/core/tests/Drupal/Tests/Core/Http/InputBagTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..43b24db1298cf139b5283394ad2901a6f67fd453
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Http/InputBagTest.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\Tests\Core\Http;
+
+use Drupal\Core\Http\InputBag;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Http\InputBag
+ *
+ * @group Http
+ */
+class InputBagTest extends UnitTestCase {
+
+  /**
+   * @covers ::all
+   */
+  public function testAll() {
+    $input = [
+      'bad' => 'bad',
+      'good' => ['good'],
+    ];
+    $input_bag = new InputBag();
+    $input_bag->replace($input);
+    $this->assertSame($input_bag->all(), $input);
+    $this->assertSame($input_bag->all('good'), ['good']);
+    $this->expectException(\UnexpectedValueException::class);
+    $input_bag->all('bad');
+  }
+
+}