Upload library won't accept midi files

On my website, some users should be able to upload midi-files (mime-type: audio/mid).
I set up my controller to load the upload library. In my configuration I have a setting $config['allowed_types'] = ...
I tried 'mid|midi'. Also tried array('audio/mid','audio/midi'). In either case, I get an error 'The filetype you are attempting to upload is not allowed.'
I echoed the file-type with $error = array('error' => $this->upload->display_errors()). This showed the file-type of the upload file: 'audio/mid', which is in my array of allowed_types. Why is it rejected anyway?

That is not a correct mime-type, .mid files should be audio/midi (notice i)

That is not a correct mime-type, .mid files should be audio/midi (notice i)

Hi Gadelat, I tried that. Like I wrote before:
I tried 'mid|midi'. Also tried array('audio/mid','audio/midi'). In either case, I get an error 'The filetype you are attempting to upload is not allowed.'