how to permit the "?" and "=" in the url ?

[eluser]quasiperfect[/eluser]
i tried to add the chars to the permitted uri in the config

Code:

$config['permitted_uri_chars'] = 'a-z 0-9~%.:_\-?=';

but i get a error

Code:

A PHP Error was encountered

Severity: Warning

Message: preg_match() [function.preg-match]: Compilation failed: range out of order in character class at offset 20

Filename: libraries/URI.php

Line Number: 189

An Error Was Encountered

The URI you submitted has disallowed characters.