diff -u b/core/modules/media/src/Plugin/media/Handler/File.php b/core/modules/media/src/Plugin/media/Handler/File.php
--- b/core/modules/media/src/Plugin/media/Handler/File.php
+++ b/core/modules/media/src/Plugin/media/Handler/File.php
@@ -31,7 +31,7 @@
    * {@inheritdoc}
    */
   public function getField(MediaInterface $media, $name) {
-    $file = $this->getSourceFieldValue($media);
+    $file = $this->getSourceFile($media);
 
     switch ($name) {
       case 'mime':
@@ -49,14 +49,14 @@
    * {@inheritdoc}
    */
   public function getThumbnail(MediaInterface $media) {
-    $file = $this->getSourceFieldValue($media);
+    $file = $this->getSourceFile($media);
     $icon_base = $this->configFactory->get('media.settings')->get('icon_base');
     $thumbnail = FALSE;
 
     // We try to magically use the most specific icon present in the $icon_base
-    // directory, based on the mime information. For instance, if an icon file
+    // directory, based on the MIME information. For instance, if an icon file
     // named "pdf.png" is present, it will be used if the file matches this
-    // mime type.
+    // MIME type.
     if ($file) {
       $mimetype = $file->getMimeType();
       $mimetype = explode('/', $mimetype);
@@ -79,7 +79,7 @@
    */
   public function getDefaultName(MediaInterface $media) {
     // The default name will be the filename of the source_field.
-    return $this->getSourceFieldValue($media)->getFilename();
+    return $this->getSourceFile($media)->getFilename();
   }
 
   /**
@@ -90,8 +90,12 @@
    *
    * @return \Drupal\file\FileInterface
    *   The file entity present in the source field.
+   *
+   * @throws \RuntimeException
+   *   If the source field for the handler is not defined, or if the
+   *   source field does not contain a file entity.
    */
-  protected function getSourceFieldValue(MediaInterface $media) {
+  protected function getSourceFile(MediaInterface $media) {
     $source_field = $this->configuration['source_field'];
 
     if (empty($source_field)) {