install() got an unexpected keyword argument 'checksum'

I've got the following install hook:

    @hooks.hook('install')
    def install():
        install_remote(
            source='http://example.org/archive.tgz',
            dest='/usr/share/something',
            checksum='1234567890',
            hash_type='sha1',
        )

This works without any issues when deploying for Precise but fails with the following exception in Trusty:

    Traceback (most recent call last):
      File "hooks/install", line 147, in <module>
        hooks.execute(argv)
      File "/var/lib/juju/agents/unit-something-0/charm/hooks/charmhelpers/core/hookenv.py", line 704, in execute
        self._hooks[hook_name]()
      File "hooks/install", line 86, in install
        hash_type='sha1',
      File "/var/lib/juju/agents/unit-something-0/charm/hooks/charmhelpers/fetch/__init__.py", line 388, in install_remote
        installed_to = handler.install(source, *args, **kwargs)
    TypeError: install() got an unexpected keyword argument 'checksum'

I'm using Juju directly from the stable PPA (1.24.6-vivid-amd64) and the latest revision of charm-helpers directly from lp:charm-helpers.