Error: Cannot redeclare… using Unzip-library

[eluser]Ornis[/eluser]
The following implemention of Unzip-library:

<?php
Class Unzip extends Controller {

function unzip() {
parent::controller() ;
}


function index() {
$this->load->library('Unzip');

// Give it one parameter and it will extract to the same folder
$this->unzip->extract('./img_maptiles/17.zip');

// or specify a destination directory
$this->unzip->extract('./img_maptiles/mydest/');

}
}

produces an error that I can't understand:

Fatal error: Cannot redeclare class Unzip in /home/httpd/vhosts/avimonitoring.ch/httpdocs/ci/system/application/libraries/Unzip.php on line 22

What do I miss here? Thanks for your help.

Martin