diff --git a/library/Icinga/Web/Response.php b/library/Icinga/Web/Response.php
index cdb377efd..d96972de6 100644
--- a/library/Icinga/Web/Response.php
+++ b/library/Icinga/Web/Response.php
@@ -275,7 +275,7 @@ class Response extends Zend_Controller_Response_Http
             }
         }
 
-        $this->setHeader("Content-Type", $this->getContentType(), true);
+        $this->setHeader('Content-Type', $this->getContentType(), false);
     }
 
     /**