rbenv Ruby versions and gems

When installing a new Ruby version with rbenv, the new versions won’t generally have appropriates gems to go with. However Trying to install the appropriate gems seems to work at first but when trying to invoke said gem, it often results in the following error (for example with bundle):

rbenv: bundle: command not found

The `bundle' command exists in these Ruby versions:

The following commands seems to fix things, although not always it seems:

gem update --system

Throwing in a rbenv rehash after installing the gem does not hurt as well.