Meteor checkbox group - At least one checkbox selected

This is the checkboxes i have so far. I would like to have at least one checkbox checked all the time - how can this be accomplished?

HTML:

    <form>
        <ul>
            {{#each checkbox}}
            <li>
                <input type="checkbox" checked="{{checked}}" class="toggle-checked"> {{name}}: {{checked}}
            </li>
            {{/each}}
        </ul>
    </form>

JS:

    Cbtest = new Mongo.Collection('cbtest');

    Template.checkbox.helpers({
        checkbox: function () {
            return Cbtest.find();
        }
    });

    Template.checkbox.events({
        "click .toggle-checked": function () {
           var self = this;
            Meteor.call("setChecked", self._id, !self.checked);
        }
    });

    Meteor.methods({
        setChecked: function (checkboxId, setChecked) {
            Cbtest.update(checkboxId, {
                $set: {
                    checked: setChecked
                }
            });
        }
    });

I'd like to avoid jquery and stick with javascript and underscorejs solely.

Thanks in advance! Vin