functions.php Pipe

I am trying to add this code to the functions.php so I may upload EPUB|MOBI files as follows:

function addUploadMimes($mimes) {
$mimes = array_merge($mimes, array(
‘epub|mobi’ => ‘application/octet-stream’
));
return $mimes;
}
add_filter(‘upload_mimes’, ‘addUploadMimes’);

However it keeps conflicting with your hook, how do I correct for this so I can upload the aforementioned files?
Thank you