diff --git a/typo3/sysext/core/Classes/Http/HtmlResponse.php b/typo3/sysext/core/Classes/Http/HtmlResponse.php
index 1ae29032c9..74355e6494 100644
--- a/typo3/sysext/core/Classes/Http/HtmlResponse.php
+++ b/typo3/sysext/core/Classes/Http/HtmlResponse.php
@@ -40,7 +40,7 @@ class HtmlResponse extends Response
         // Ensure that text/html header is set, if Content-Type was not set before
         if (!$this->hasHeader('Content-Type')) {
             $this->headers['Content-Type'][] = 'text/html; charset=utf-8';
-            $this->lowercasedHeaderNames['content-type'] = 'Content-type';
+            $this->lowercasedHeaderNames['content-type'] = 'Content-Type';
         }
     }
 }
diff --git a/typo3/sysext/core/Classes/Http/JsonResponse.php b/typo3/sysext/core/Classes/Http/JsonResponse.php
index 09f7ba7eb6..f240786e14 100644
--- a/typo3/sysext/core/Classes/Http/JsonResponse.php
+++ b/typo3/sysext/core/Classes/Http/JsonResponse.php
@@ -67,7 +67,7 @@ class JsonResponse extends Response
         // Ensure that application/json header is set, if Content-Type was not set before
         if (!$this->hasHeader('Content-Type')) {
             $this->headers['Content-Type'][] = 'application/json; charset=utf-8';
-            $this->lowercasedHeaderNames['content-type'] = 'Content-type';
+            $this->lowercasedHeaderNames['content-type'] = 'Content-Type';
         }
     }