RSS to exclude 1 category from feed

I would like to set my RSS to ignore one of the categories. I tried changing in wp-rss2.php

$items_count = 0; if ($posts) { foreach ($posts as $post) { start_wp(); ?>

to

$items_count = 0; if ($posts) { if (!in_category(‘1’)) { foreach ($posts as $post) { start_wp(); ?>

But it is still sending even the posts of category 1 to the RSS Feed. How can I set it to exclude a category?