Set Meteor Accounts signup field checkbox default to 'checked'

I need to add a checkbox to Meteor Accounts Sign-up form.
From the docs:

AccountsTemplates.addFields([
  {
    _id: 'newsletter',
    type: 'checkbox',
    displayName: 'Subscribe to newsletter',
    options: {
      checked: true // this does not work
    }
  }
]);

Has anyone done this before?

I’ve also tried

Template.atForm.onRendered()

and

Tracker.autorun => AccountsTemplates.getState() == "signUp" (...)

but no luck :frowning: