diff --git a/core/core.services.yml b/core/core.services.yml
index 1bceb3c..345a54e 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1558,7 +1558,6 @@ services:
     class: Drupal\Core\File\MimeType\MimeTypeMapper
     calls:
       - [alterMapping, ['@module_handler']]
-    lazy: true
   file.mime_type.guesser:
     class: Drupal\Core\File\MimeType\MimeTypeGuesser
     arguments: ['@stream_wrapper_manager']
diff --git a/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php b/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php
index 0c9d097..1e8578a 100644
--- a/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php
+++ b/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php
@@ -39,7 +39,7 @@ public function alterMapping(ModuleHandlerInterface $module_handler);
    *
    * @return $this
    */
-  public function setMapping($mimetype, $extension);
+  public function setMapping(array $mapping);
 
   /**
    * Adds a mapping between a MIME type and an extension.
diff --git a/core/lib/Drupal/Core/ProxyClass/File/MimeType/MimeTypeMapper.php b/core/lib/Drupal/Core/ProxyClass/File/MimeType/MimeTypeMapper.php
deleted file mode 100644
index 7066840..0000000
--- a/core/lib/Drupal/Core/ProxyClass/File/MimeType/MimeTypeMapper.php
+++ /dev/null
@@ -1,136 +0,0 @@
-<?php
-// @codingStandardsIgnoreFile
-
-/**
- * This file was generated via php core/scripts/generate-proxy-class.php 'Drupal\Core\File\MimeType\MimeTypeMapper' "core/lib/Drupal/Core".
- */
-
-namespace Drupal\Core\ProxyClass\File\MimeType {
-
-    /**
-     * Provides a proxy class for \Drupal\Core\File\MimeType\MimeTypeMapper.
-     *
-     * @see \Drupal\Component\ProxyBuilder
-     */
-    class MimeTypeMapper implements \Drupal\Core\File\MimeType\MimeTypeMapperInterface
-    {
-
-        use \Drupal\Core\DependencyInjection\DependencySerializationTrait;
-
-        /**
-         * The id of the original proxied service.
-         *
-         * @var string
-         */
-        protected $drupalProxyOriginalServiceId;
-
-        /**
-         * The real proxied service, after it was lazy loaded.
-         *
-         * @var \Drupal\Core\File\MimeType\MimeTypeMapper
-         */
-        protected $service;
-
-        /**
-         * The service container.
-         *
-         * @var \Symfony\Component\DependencyInjection\ContainerInterface
-         */
-        protected $container;
-
-        /**
-         * Constructs a ProxyClass Drupal proxy object.
-         *
-         * @param \Symfony\Component\DependencyInjection\ContainerInterface $container
-         *   The container.
-         * @param string $drupal_proxy_original_service_id
-         *   The service ID of the original service.
-         */
-        public function __construct(\Symfony\Component\DependencyInjection\ContainerInterface $container, $drupal_proxy_original_service_id)
-        {
-            $this->container = $container;
-            $this->drupalProxyOriginalServiceId = $drupal_proxy_original_service_id;
-        }
-
-        /**
-         * Lazy loads the real service from the container.
-         *
-         * @return object
-         *   Returns the constructed real service.
-         */
-        protected function lazyLoadItself()
-        {
-            if (!isset($this->service)) {
-                $this->service = $this->container->get($this->drupalProxyOriginalServiceId);
-            }
-
-            return $this->service;
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function alterMapping(\Drupal\Core\Extension\ModuleHandlerInterface $module_handler)
-        {
-            return $this->lazyLoadItself()->alterMapping($module_handler);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function setMapping(array $mapping)
-        {
-            return $this->lazyLoadItself()->setMapping($mapping);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function addMapping($mimetype, $extension)
-        {
-            return $this->lazyLoadItself()->addMapping($mimetype, $extension);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function removeMapping($extension)
-        {
-            return $this->lazyLoadItself()->removeMapping($extension);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function removeMimeType($mimetype)
-        {
-            return $this->lazyLoadItself()->removeMimeType($mimetype);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function getMimeTypes()
-        {
-            return $this->lazyLoadItself()->getMimeTypes();
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function getMimeTypeForExtension($extension)
-        {
-            return $this->lazyLoadItself()->getMimeTypeForExtension($extension);
-        }
-
-        /**
-         * {@inheritdoc}
-         */
-        public function getExtensionsForMimeType($mimetype)
-        {
-            return $this->lazyLoadItself()->getExtensionsForMimeType($mimetype);
-        }
-
-    }
-
-}
diff --git a/core/tests/Drupal/KernelTests/Core/File/MimeTypeTest.php b/core/tests/Drupal/KernelTests/Core/File/MimeTypeTest.php
index f507aed..9979d9c 100644
--- a/core/tests/Drupal/KernelTests/Core/File/MimeTypeTest.php
+++ b/core/tests/Drupal/KernelTests/Core/File/MimeTypeTest.php
@@ -89,6 +89,7 @@ public function testFileMimeTypeDetection() {
     // Now test that MIME types added via alter hook or directly via
     // MimeTypeMapper::addMapping are present in the list returned by
     // MimeTypeMapper::getMimeTypes.
+    $mime_type_mapper = $this->container->get('file.mime_type.mapper');
     $test_case = [
       'bar/foo' => ['jar'],
       'fox/trot' => ['jpg'],