Migration - Unknown directive registerConfig when using collective.jsonmigrator

This is my zcml file

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:transmogrifier="http://namespaces.plone.org/transmogrifier"
    i18n_domain="collective.transmogrifier">

<transmogrifier:registerConfig
    name="mycontent"
    title="My Content"
    description="This is content from the Plone 4 site"
    configuration="my.site:jsonsource.cfg"
    />
</configure>

I get the following error:

ConfigurationError: ('Unknown directive', u'http://namespaces.plone.org/transmogrifier', u'registerConfig')

I double checked and collective.transmogrifier is installed (it's a dependency of collective.jsonmigrator, which I'm using).

After a bit more reading around I found that I needed to include collective.transmogrifier explicitly as a package in my zcml.

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:transmogrifier="http://namespaces.plone.org/transmogrifier"
    i18n_domain="collective.transmogrifier">

  <include package="collective.transmogrifier" />
  <include package="collective.transmogrifier" file="meta.zcml" />

<transmogrifier:registerConfig
    name="mycontent"
    title="My Content"
    description="This is content from the Plone 4 site"
    configuration="my.site:jsonsource.cfg"
    />
</configure>

I haven't tested this, but I suspect it might also work if I added collective.transmogrifier to the setup.py of
my package as a dependency.

For the sake of my future self the file above is named transmogrify.zcml and I call it from my main configure.zcml using an include:

...
<include file=transmogrify.zcml />
...