RTC: How to prevent users from assigning themselves to a role not intended for them?

We have a role - Defect Synchronizer defined in our process and it has permissions that we don't want our normal users to have. However, users could still (accidentally) assign the role to themselves and able to make changes they really shouldn't make. So my question is if we could prevent users from assigning themselves or if there is another workaround.

Thanks.