Redirect to custom 404 page when somebody enters random or misspelled unexistent controller in URL

[eluser]luismartin[/eluser]
Considering this URL:

http://www.mysite.com/history

if I misspell the controller, or I enter a random one, like this

http://www.mysite.com/sdsdrgerg

I get this error (with a 'development' environment established):

Fatal error: Class 'CI_Controller' not found in C:\path\to\site\system\core\CodeIgniter.php on line 231

I'd like to redirect any bad request to my site to a custom 404 page, while keeping the 404 http code.

Any suggestion appreciated.