diff --git a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
index 82be021..19cdf98 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
@@ -81,6 +83,10 @@ public function onRespond(FilterResponseEvent $event) {
       $response->headers->set($name, $value, FALSE);
     }
 
+    // Currently it is not possible to cache some types of responses. Therefore
+    // exclude binary file responses (generated files, e.g. images with image
+    // styles) and streamed responses (files directly read from the disk).
+    // see: https://github.com/symfony/symfony/issues/9128#issuecomment-25088678
     $is_cacheable = drupal_page_is_cacheable() && !($response instanceof BinaryFileResponse) && !($response instanceof StreamedResponse);
 
     // Add headers necessary to specify whether the response should be cached by
diff --git a/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php b/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php
index 8baa3f2..51ae9ce 100644
--- a/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php
+++ b/core/modules/file/lib/Drupal/file/Tests/DownloadTest.php
@@ -53,7 +53,7 @@ function testPublicFileTransfer() {
   /**
    * Test the private file transfer system.
    */
-  public function testPrivateFileTransfer() {
+  public function testPrivateFileTransferWithoutPageCache() {
     $this->doPrivateFileTransferTest();
   }