core/modules/media/media.module                    | 16 ++++++++
 .../tests/src/Functional/MediaResourceTest.php     | 47 ++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/core/modules/media/media.module b/core/modules/media/media.module
index eeb2ac1..9faf7c8 100644
--- a/core/modules/media/media.module
+++ b/core/modules/media/media.module
@@ -48,6 +48,22 @@ function media_theme() {
 }
 
 /**
+ * Implements hook_rest_resource_alter().
+ *
+ * The normalization of Media and Media Type entities was never considered
+ * during their development. Rather than allowing them to fall back to defaults
+ * for their normalizations (and hence serializations), this excludes them from
+ * being exposed as REST resources. This is done to ensure we don't let clients
+ * be developed against the default normalizations, which are known to contain
+ * gaps especially for file handling, and hence are guaranteed to break BC.
+ *
+ * @todo Remove this in https://www.drupal.org/node/2895573
+ */
+function media_rest_resource_alter(&$definitions) {
+  unset($definitions['entity:media'], $definitions['entity:media_type']);
+}
+
+/**
  * Implements hook_entity_operation_alter().
  *
  * Fix broken operations array in field UI for entities with restricted access.
diff --git a/core/modules/media/tests/src/Functional/MediaResourceTest.php b/core/modules/media/tests/src/Functional/MediaResourceTest.php
new file mode 100644
index 0000000..8e57306
--- /dev/null
+++ b/core/modules/media/tests/src/Functional/MediaResourceTest.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\Tests\media\Functional;
+
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+use Drupal\rest\Entity\RestResourceConfig;
+use Drupal\rest\RestResourceConfigInterface;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * @group media
+ *
+ * @todo Remove this in https://www.drupal.org/node/2895573
+ */
+class MediaResourceTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['rest', 'media'];
+
+  /**
+   * @dataProvider providerTestEnableMediaEntityType
+   */
+  public function testEnableMediaResource($entity_type_id) {
+    $this->setExpectedException(PluginNotFoundException::class, 'The "entity:' . $entity_type_id . '" plugin does not exist.');
+    RestResourceConfig::create([
+      'id' => 'entity.' . $entity_type_id,
+      'granularity' => RestResourceConfigInterface::RESOURCE_GRANULARITY,
+      'configuration' => [
+        'methods' => ['GET'],
+        'formats' => ['json'],
+        'authentication' => ['cookie'],
+      ],
+    ])
+      ->enable()
+      ->save();
+  }
+
+  public function providerTestEnableMediaEntityType() {
+    return [
+      ['media'],
+      ['media_type'],
+    ];
+  }
+
+}