Command-line linguist throws NoMethodError “undefined method instrument”

[roryokane]

I just installed Linguist and tried to run linguist on the directory of a software project cloned from GitHub. Straight away, it throws a NoMethodError:

undefined method `instrument' for Linguist:Module (NoMethodError)

A summarized transcript, including a stack trace:

$ git clone git@github.com:evalEmpire/perl5i.git
Cloning into 'perl5i'...
…
$ rbenv version
2.1.4 (set by /Users/roryokane/.ruby-version)
$ gem install github-linguist
…
Fetching: github-linguist-4.4.3.gem (100%)
Successfully installed github-linguist-4.4.3
…
4 gems installed
$ linguist perl5i/
/Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/language.rb:108:in `detect': undefined method `instrument' for Linguist:Module (NoMethodError)
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/blob_helper.rb:328:in `language'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/lazy_blob.rb:54:in `language'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/blob_helper.rb:343:in `include_in_language_stats?'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/repository.rb:159:in `block in compute_stats'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/repository.rb:145:in `each_delta'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/repository.rb:145:in `compute_stats'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/repository.rb:113:in `cache'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/lib/linguist/repository.rb:65:in `languages'
    from /Users/roryokane/.rbenv/versions/2.1.4/lib/ruby/gems/2.1.0/gems/github-linguist-4.4.3/bin/linguist:25:in `<top (required)>'
    from /Users/roryokane/.rbenv/versions/2.1.4/bin/linguist:23:in `load'
    from /Users/roryokane/.rbenv/versions/2.1.4/bin/linguist:23:in `<main>'

I still get the error if I cd into perl5i and then run linguist without passing a directory argument. I also get the error if I pass --breakdown to linguist.