diff --git a/src/Controller/FileUpload.php b/src/Controller/FileUpload.php
index 6c69ca0..5e87ef8 100644
--- a/src/Controller/FileUpload.php
+++ b/src/Controller/FileUpload.php
@@ -111,6 +111,9 @@ class FileUpload {
    *   Thrown when there are validation errors.
    * @throws \Drupal\Core\Entity\EntityStorageException
    *   Thrown if the upload's target resource could not be saved.
+   * @throws \Exception
+   *   Thrown if an exception occurs during a subrequest to fetch the newly
+   *   created file entity.
    */
   public function handleFileUploadForExistingResource(Request $request, ResourceType $resource_type, $file_field_name, FieldableEntityInterface $entity) {
     $field_definition = $this->validateAndLoadFieldDefinition($resource_type->getEntityTypeId(), $resource_type->getBundle(), $file_field_name);
diff --git a/src/ForwardCompatibility/FileUploader.php b/src/ForwardCompatibility/FileUploader.php
index 80e623d..3734daf 100644
--- a/src/ForwardCompatibility/FileUploader.php
+++ b/src/ForwardCompatibility/FileUploader.php
@@ -196,12 +196,10 @@ class FileUploader implements FileUploaderInterface {
    */
   public static function validateAndParseContentDispositionHeader(Request $request) {
     // First, check the header exists.
-    if (!$request->headers->has('content-disposition')) {
+    if (!$request->headers->has('content-disposition') || !($content_disposition = $request->headers->get('content-disposition'))) {
       throw new BadRequestHttpException('"Content-Disposition" header is required. A file name in the format "filename=FILENAME" must be provided.');
     }
 
-    $content_disposition = $request->headers->get('content-disposition');
-
     // Parse the header value. This regex does not allow an empty filename.
     // i.e. 'filename=""'. This also matches on a word boundary so other keys
     // like 'not_a_filename' don't work.
diff --git a/tests/src/Functional/FileUploadTest.php b/tests/src/Functional/FileUploadTest.php
index 00b81fe..94d93bd 100644
--- a/tests/src/Functional/FileUploadTest.php
+++ b/tests/src/Functional/FileUploadTest.php
@@ -747,6 +747,8 @@ class FileUploadTest extends ResourceTestBase {
       'Content-Type' => 'application/octet-stream',
       // Set the required Content-Disposition header for the file name.
       'Content-Disposition' => 'file; filename="example.txt"',
+      // Set the required JSON:API Accept header.
+      'Accept' => 'application/vnd.api+json',
     ];
     $request_options[RequestOptions::BODY] = $file_contents;
     $request_options = NestedArray::mergeDeep($request_options, $this->getAuthenticationRequestOptions());