Preventing illegal characters in username

[XFFA.IR Bot]

Hello
Quite a few of our users are recently changing their usernames to usernames containing emojis and other unicode characters.
Is there a way to prevent that?

I don't really mind them using those characters, but we get server errors regarding those changes:
XF\Db\Exception: MySQL query error [1267]: Illegal mix of collations (utf8mb3_general_ci,IMPLICIT) and (utf8mb4_general_ci,COERCIBLE) for operation '='src/XF/Db/AbstractStatement.php:230

Thanks!

Edit:
I found @AndyB...

لطفا گزینه ورود یا ثبت‌نام را انتخاب کنید تا پیوندها برای شما قابل نمایش شوند