Attachment_fu won't display content-type validation errors

I’m getting this weird behavior from attachment_fu… the error messages
displayed with <%= error_messages_for ‘picture’ %> won’t work for the
“content_type” field. It works for the filename and the size. And when I
try to upload a file type that is invalid, the file get rejected like it
is supposed to but I don’t see the error message at the top.

Am I supposed to implement it myself?

Thx in advance.