diff --git a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
index 7da48aa..4728c52 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
@@ -116,10 +116,10 @@ public function onRespond(FilterResponseEvent $event) {
     $response->headers->set('X-Frame-Options', 'SAMEORIGIN', FALSE);
 
     // If the current response isn't an implementation of the
-    // CacheableResponseInterface, we're trusting that a Response is either
-    // explicitly not cacheable or that caching headers are already set from
+    // CacheableResponseInterface, we assume that a Response is either
+    // explicitly not cacheable or that caching headers are already set in
     // another place.
-    if (!($response instanceof CacheableResponseInterface)) {
+    if (!$response instanceof CacheableResponseInterface) {
       if (!$this->isCacheControlCustomized($response)) {
         $this->setResponseNotCacheable($response, $request);
       }
diff --git a/core/modules/image/src/Controller/ImageStyleDownloadController.php b/core/modules/image/src/Controller/ImageStyleDownloadController.php
index d23d483..7b67072 100644
--- a/core/modules/image/src/Controller/ImageStyleDownloadController.php
+++ b/core/modules/image/src/Controller/ImageStyleDownloadController.php
@@ -126,8 +126,10 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
         $response = parent::download($request, $scheme);
 
         if ($response instanceof BinaryFileResponse) {
+          // The expires header is usually set in the finish response subscriber
+          // but not for images so we're setting it here.
           $response->headers->add([
-            'Expires' => \DateTime::createFromFormat('j-M-Y H:i:s T', '19-Nov-1978 05:00:00 GMT')->format('D, d M Y H:i:s T'),
+            'Expires' => \DateTime::createFromFormat('D, d M Y H:i:s T', 'Sun, 19 Nov 1978 05:00:00 GMT')->format('D, d M Y H:i:s T')
           ]);
         }
         return $response;
@@ -181,10 +183,12 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     if ($success) {
       $image = $this->imageFactory->get($derivative_uri);
       $uri = $image->getSource();
+      // The expires header is usually set in the finish response subscriber
+      // but not for images so we're setting it here.
       $headers += array(
         'Content-Type' => $image->getMimeType(),
         'Content-Length' => $image->getFileSize(),
-        'Expires' => \DateTime::createFromFormat('j-M-Y H:i:s T', '19-Nov-1978 05:00:00 GMT')->format('D, d M Y H:i:s T'),
+        'Expires' => \DateTime::createFromFormat('D, d M Y H:i:s T', 'Sun, 19 Nov 1978 05:00:00 GMT')->format('D, d M Y H:i:s T'),
       );
       return new BinaryFileResponse($uri, 200, $headers, FALSE);
     }
diff --git a/core/modules/page_cache/src/Tests/PageCacheTest.php b/core/modules/page_cache/src/Tests/PageCacheTest.php
index 421ebf1..a2278e7 100644
--- a/core/modules/page_cache/src/Tests/PageCacheTest.php
+++ b/core/modules/page_cache/src/Tests/PageCacheTest.php
@@ -407,10 +407,10 @@ public function testFormImmutability() {
   }
 
   /**
-   * Tests cacheability of a CacheableResponse
+   * Tests cacheability of a CacheableResponse.
    *
-   * Tests the difference between having a controller return a normal Response
-   * object versus returning a Response object that implements the
+   * Tests the difference between having a controller return a plain Symfony
+   * Response object versus returning a Response object that implements the
    * CacheableResponseInterface.
    */
   public function testCacheableResponseResponses() {
@@ -439,7 +439,7 @@ public function testCacheableResponseResponses() {
     $this->assertEqual($this->drupalGetHeader('Cache-Control'), 'max-age=300, public', 'Cache-Control header was sent.');
 
     // Uninstall page cache. This should flush all caches so the next call to a
-    // previously cache page should be a miss now.
+    // previously cached page should be a miss now.
     $this->container->get('module_installer')
       ->uninstall(['page_cache']);
 
diff --git a/core/modules/rest/src/RequestHandler.php b/core/modules/rest/src/RequestHandler.php
index 9cb413e..d3b69b5 100644
--- a/core/modules/rest/src/RequestHandler.php
+++ b/core/modules/rest/src/RequestHandler.php
@@ -68,7 +68,7 @@ public function handle(RouteMatchInterface $route_match, Request $request) {
         catch (UnexpectedValueException $e) {
           $error['error'] = $e->getMessage();
           $content = $serializer->serialize($error, $format);
-          return new CacheableResponse($content, 400, ['Content-Type' => $request->getMimeType($format)]);
+          return new Response($content, 400, ['Content-Type' => $request->getMimeType($format)]);
         }
       }
       else {
@@ -101,7 +101,7 @@ public function handle(RouteMatchInterface $route_match, Request $request) {
       // Add the default content type, but only if the headers from the
       // exception have not specified it already.
       $headers = $e->getHeaders() + array('Content-Type' => $request->getMimeType($format));
-      return new CacheableResponse($content, $e->getStatusCode(), $headers);
+      return new Response($content, $e->getStatusCode(), $headers);
     }
 
     // Serialize the outgoing data for the response, if available.