Unexpected token error when migrating to native classes for components

I upgraded to Ember 3.11 and I want to start using native classes for my components. When I change a component class to something similar like:

    export default class MyClassName extends BaseComponent {

        myFieldName;

I get a build error "Parsing error: Unexpected token ;" because of the class field.

Ideas how to make sure ember-cli doesn't complain about the new syntax are more than welcome.

Thanks