Preventing impostors from registering - matching UTF8 chars that look exactly the same, but have a different code

I have a problem with users registering with usernames that LOOK exactly the same as existing users' by using UTF8 characters which, while being encoded differently, look the same.

Example:
Maximus
Mаximus

They look the same, don't they? But this are 2 separate users: one using proper 'a' char, and the second using char that gets urlencoded as %D0%B0

Is there any way I could prevent it, preferably in a way that would not prevent me from using non-latin1 characters in usernames?