Nginx limit_conn in IF statement?

How to make possible something like this?

location /download/ {
limit_conn addr 2;

if ($arg_C) {
limit_conn addr 1;
}
}

Gives me an error:
Restarting nginx: nginx: [emerg] "limit_conn" directive is not allowed here in /etc/nginx/sites-enabled/www.mypage.com:60