diff --git a/core/modules/media/src/MediaTypeForm.php b/core/modules/media/src/MediaTypeForm.php
index d6965560160e94d88ae2f80fec8fc1d33861e65c..93fed859ed5779aa1ea7ea347c2a48b835358472 100644
--- a/core/modules/media/src/MediaTypeForm.php
+++ b/core/modules/media/src/MediaTypeForm.php
@@ -118,7 +118,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#attributes' => ['id' => 'source-dependent'],
     ];
 
-    if ($source) {
+    if (!$this->entity->isNew()) {
       $source_description = $this->t('<em>The media source cannot be changed after the media type is created.</em>');
     }
     else {
@@ -134,7 +134,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#required' => TRUE,
       // Once the media type is created, its source plugin cannot be changed
       // anymore.
-      '#disabled' => !empty($source),
+      '#disabled' => !$this->entity->isNew(),
     ];
 
     if ($source) {
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php b/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php
index 207b542f95f6e000f72a47019ddc743dc12e6da5..42e3511f315b9d1b8a94f43e89663ecd4d932540 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaTypeCreationTest.php
@@ -11,6 +11,45 @@
  */
 class MediaTypeCreationTest extends MediaJavascriptTestBase {
 
+  /**
+   * Tests the source field behavior on the add media type form.
+   */
+  public function testSourceChangeOnMediaTypeCreationForm() {
+    $session = $this->getSession();
+    $page = $session->getPage();
+    $assert_session = $this->assertSession();
+
+    $label = 'Type with Default Field';
+    $mediaTypeMachineName = str_replace(' ', '_', strtolower($label));
+
+    $this->drupalGet('admin/structure/media/add');
+
+    // Fill in a label to the media type.
+    $page->fillField('label', $label);
+    $this->assertNotEmpty(
+      $assert_session->waitForElementVisible('css', '.machine-name-value')
+    );
+
+    // Select the media source used by our media type.
+    $assert_session->selectExists('Media source')->selectOption('test_different_displays');
+    $this->assertNotEmpty(
+      $assert_session->waitForElementVisible('css', 'fieldset[data-drupal-selector="edit-source-configuration"]')
+    );
+
+    // Change the media source.
+    $assert_session->selectExists('Media source')->selectOption('test');
+    $this->assertNotEmpty(
+      $assert_session->waitForElement('css', 'fieldset[data-drupal-selector="edit-source-configuration"] .fieldset-wrapper .placeholder:contains("Text (plain)")')
+    );
+
+    $page->pressButton('Save');
+
+    // Check that source can not be changed anymore.
+    $this->drupalGet("admin/structure/media/manage/{$mediaTypeMachineName}");
+    $assert_session->pageTextContains('The media source cannot be changed after the media type is created');
+    $assert_session->fieldDisabled('Media source');
+  }
+
   /**
    * Tests the media type creation form.
    */