diff -ur image.old/src/Controller/ImageStyleDownloadController.php image/src/Controller/ImageStyleDownloadController.php
--- image.old/src/Controller/ImageStyleDownloadController.php	2016-10-26 11:56:41.606750565 +0200
+++ image/src/Controller/ImageStyleDownloadController.php	2016-10-26 12:20:12.498816191 +0200
@@ -161,8 +161,8 @@
       $image = $this->imageFactory->get($derivative_uri);
       $uri = $image->getSource();
       $headers += array(
-        'Content-Type' => $image->getMimeType(),
-        'Content-Length' => $image->getFileSize()
+        'Content-Type' => $image->getMimeType()
+        //'Content-Length' => $image->getFileSize()
       );
       // \Drupal\Core\EventSubscriber\FinishResponseSubscriber::onRespond()
       // sets response as not cacheable if the Cache-Control header is not