Perl complaining about not being able to set locale?

If you are getting this error when running Perl, usually from a ssh session:

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
       LANGUAGE = (unset),
       LC_ALL = (unset),
       LC_CTYPE = "en_US.UTF-8",
       LANG = "en_AU.UTF-8"
   are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_AU.UTF-8").

You are missing the locale mentioned in LC_CTYPE. Run:

dpkg-reconfigure locales

select the missing locale, in this case en_US.UTF-8 and generate it. Voilà, error fixed.