prevent members from changing usernames

A few members of my site have discovered a bug where if they change their username, all forum stats are reset. I would like to prevent members from changing their usernames, is there a built in option to turn this off or do I need to hack apart the profile edit page?

You can edit the profile fields by navigation to administration, builders, profiles fields, where you can remove the username field item from the edit profile section.

I can't believe I missed that.. Thank you for the refresher :)