diff --git a/core/modules/media/src/Plugin/media/Handler/File.php b/core/modules/media/src/Plugin/media/Handler/File.php
index d0b2094..ed50a11 100644
--- a/core/modules/media/src/Plugin/media/Handler/File.php
+++ b/core/modules/media/src/Plugin/media/Handler/File.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\media\Plugin\media\Handler;
 
-use Drupal\media\MediaTypeInterface;
 use Drupal\media\MediaInterface;
 use Drupal\media\MediaHandlerBase;
 
@@ -32,13 +31,8 @@ public function providedFields() {
    * {@inheritdoc}
    */
   public function getField(MediaInterface $media, $name) {
-    $source_field = $this->configuration['source_field'];
-
-    // Get the file.
-    /** @var \Drupal\file\FileInterface $file */
-    $file = $media->{$source_field}->entity;
+    $file = $this->getSourceFieldValue($media);
 
-    // Return the field.
     switch ($name) {
       case 'mime':
         return $file->getMimeType() ?: FALSE;
@@ -55,9 +49,7 @@ public function getField(MediaInterface $media, $name) {
    * {@inheritdoc}
    */
   public function thumbnail(MediaInterface $media) {
-    $source_field = $this->configuration['source_field'];
-    /** @var \Drupal\file\FileInterface $file */
-    $file = $media->{$source_field}->entity;
+    $file = $this->getSourceFieldValue($media);
     $icon_base = $this->configFactory->get('media.settings')->get('icon_base');
     $thumbnail = FALSE;
 
@@ -87,39 +79,39 @@ public function thumbnail(MediaInterface $media) {
    */
   public function getDefaultName(MediaInterface $media) {
     // The default name will be the filename of the source_field, if present.
+    $file = $this->getSourceFieldValue($media);
+    return $file->getFilename();
+  }
+
+  /**
+   * Get source field file entity.
+   *
+   * @param \Drupal\media\MediaInterface $media
+   *   The media entity.
+   *
+   * @return \Drupal\file\FileInterface
+   *   The file entity present in the source field.
+   */
+  protected function getSourceFieldValue(MediaInterface $media) {
     $source_field = $this->configuration['source_field'];
 
-    /** @var \Drupal\file\FileInterface $file */
-    if (!empty($source_field) && ($file = $media->{$source_field}->entity)) {
-      return $file->getFilename();
+    if (empty($source_field)) {
+      throw new \RuntimeException('Source field for media file handler is not defined.');
     }
 
-    return parent::getDefaultName($media);
-  }
+    $file = $media->get($source_field)->entity;
+    if (empty($file)) {
+      throw new \RuntimeException('The source field does not contain a file entity.');
+    }
 
-  /**
-   * {@inheritdoc}
-   */
-  protected function createSourceFieldStorage() {
-    return $this->entityTypeManager
-      ->getStorage('field_storage_config')
-      ->create([
-        'entity_type' => 'media',
-        'field_name' => $this->getSourceFieldName(),
-        'type' => 'file',
-      ]);
+    return $file;
   }
 
   /**
    * {@inheritdoc}
    */
-  protected function createSourceField(MediaTypeInterface $type) {
-    return $this->entityTypeManager
-      ->getStorage('field_config')
-      ->create([
-        'field_storage' => $this->getSourceFieldStorage(),
-        'bundle' => $type->id(),
-      ]);
+  protected function getSourceFieldType() {
+    return 'file';
   }
 
 }
diff --git a/core/modules/media/tests/src/FunctionalJavascript/MediaHandlerTestBase.php b/core/modules/media/tests/src/FunctionalJavascript/MediaHandlerTestBase.php
index b176020..911f339 100644
--- a/core/modules/media/tests/src/FunctionalJavascript/MediaHandlerTestBase.php
+++ b/core/modules/media/tests/src/FunctionalJavascript/MediaHandlerTestBase.php
@@ -42,8 +42,7 @@ public function createMediaTypeTest($type_name, $type_id, array $provided_fields
 
     $this->drupalGet('admin/structure/media/add');
     $page->fillField('label', $type_name);
-    // assertWaitOnAjaxRequest() doesn't work on the machine name element.
-    $session->wait(5000, "jQuery('.machine-name-value').text() === '$type_name'");
+    $this->assertJsCondition("jQuery('.machine-name-value').text() === '$type_name'");
 
     // Make sure the type is available.
     $assert_session->optionExists('handler', $type_id);