diff --git a/Neos.Flow/Classes/Http/Helper/ResponseInformationHelper.php b/Neos.Flow/Classes/Http/Helper/ResponseInformationHelper.php
index 9c7fdc0a57..1858a2b88e 100644
--- a/Neos.Flow/Classes/Http/Helper/ResponseInformationHelper.php
+++ b/Neos.Flow/Classes/Http/Helper/ResponseInformationHelper.php
@@ -228,7 +228,7 @@ public static function makeStandardsCompliant(ResponseInterface $response, Reque
             }
         }
 
-        if (!$response->hasHeader('Content-Length')) {
+        if (!$response->hasHeader('Content-Length') && $response->getBody()->getSize() !== null) {
             $response = $response->withHeader('Content-Length', $response->getBody()->getSize());
         }
 
diff --git a/Neos.Flow/Classes/Mvc/ActionResponse.php b/Neos.Flow/Classes/Mvc/ActionResponse.php
index ded3df3dfc..f52ec1a0ac 100644
--- a/Neos.Flow/Classes/Mvc/ActionResponse.php
+++ b/Neos.Flow/Classes/Mvc/ActionResponse.php
@@ -345,6 +345,7 @@ public function buildHttpResponse(): ResponseInterface
      */
     private function hasContent(): bool
     {
-        return $this->content->getSize() > 0;
+        $contentSize = $this->content->getSize();
+        return $contentSize === null || $contentSize > 0;
     }
 }