Sorry, I forgot to add the following part of the config (from server's block):

# Static files location
location ~* ^.+\.(jpg|jpeg|gif|png|ico|css|zip|tgz|gz|rar|bz2|doc|xls|exe|pdf|ppt|txt|tar|wav|bmp|rtf|js)$ {
if ($args ~* "^download") {
add_header Content-Disposition "attachment; filename=$1";
}

expires 30d;
root /home/www/domain.com;
}