diff --git a/modules/system/classes/ErrorHandler.php b/modules/system/classes/ErrorHandler.php
index <HASH>..<HASH> 100644
--- a/modules/system/classes/ErrorHandler.php
+++ b/modules/system/classes/ErrorHandler.php
@@ -49,7 +49,7 @@ class ErrorHandler extends ErrorHandlerBase
 
         // Route to the CMS error page.
         $controller = new Controller($theme);
-        return $controller->run('/error');
+        return $controller->run('/error')->getContent();
     }
 
     /**
Fixed custom error pages outputting headers

If we don't have this method called, then the controller returns an object. From then on, [Symfony converts this object in to a string](<URL>` returns a string and everything works as expected.