diff --git a/src/opnsense/mvc/app/library/OPNsense/Mvc/Response.php b/src/opnsense/mvc/app/library/OPNsense/Mvc/Response.php
index 4efd7b606..b003b25b5 100644
--- a/src/opnsense/mvc/app/library/OPNsense/Mvc/Response.php
+++ b/src/opnsense/mvc/app/library/OPNsense/Mvc/Response.php
@@ -61,7 +61,7 @@ class Response
      * @param string|null $charset optional characterset
      * @return void
      */
-    public function setContentType(string $contentType, ?string $charset): void
+    public function setContentType(string $contentType, ?string $charset = null): void
     {
         if (!empty($charset)) {
             $contentType .= '; charset=' . $charset;