diff --git a/core/modules/media/tests/src/Functional/MediaSettingsTest.php b/core/modules/media/tests/src/Functional/MediaSettingsTest.php
index 64b85db250..06df4a9f9a 100644
--- a/core/modules/media/tests/src/Functional/MediaSettingsTest.php
+++ b/core/modules/media/tests/src/Functional/MediaSettingsTest.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\Tests\media\Functional;
 
+use Drupal\Core\Url;
+
 /**
  * Testing the media settings.
  *
@@ -19,7 +21,10 @@ class MediaSettingsTest extends MediaFunctionalTestBase {
    */
   protected function setUp(): void {
     parent::setUp();
-    $this->drupalLogin($this->createUser(['administer site configuration']));
+    $this->drupalLogin($this->createUser([
+      'administer site configuration',
+      'administer media',
+    ]));
   }
 
   /**
@@ -37,4 +42,25 @@ public function testStatusPage() {
     $assert_session->pageTextContains('It is potentially insecure to display oEmbed content in a frame');
   }
 
+  /**
+   * Tests that the media settings form stores a `null` iFrame domain.
+   */
+  public function testSettingsForm(): void {
+    $assert_session = $this->assertSession();
+
+    $this->assertNull($this->config('media.settings')->get('iframe_domain'));
+    $this->drupalGet(Url::fromRoute('media.settings'));
+    $assert_session->fieldExists('iframe_domain');
+
+    // Explicitly submitting an empty string does not result in the
+    // `iframe_domain` property getting set to the empty string: it is converted
+    // to `null` to comply with the config schema.
+    // @see \Drupal\media\Form\MediaSettingsForm::submitForm()
+    $this->submitForm([
+      'iframe_domain' => '',
+    ], 'Save configuration');
+    $assert_session->statusMessageContains('The configuration options have been saved.', 'status');
+    $this->assertNull($this->config('media.settings')->get('iframe_domain'));
+  }
+
 }