header for each category

Hi everyone.
when i put this code in the index.php file of my template:

<?php if (is_category('Commander')) {
get_header('commander');
} else {
get_header();
} ?>

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it wont work. i tried to test if the “header-commander” by getting this header as a default, so the problem is in the IF section.
how can i solve this?
thanks.