Ember.js: how do I override one of my superclass's actions in a component?

This is Ember.js 2.11. If I have a Component:

app/components/a/component.js

export default EmberComponent.extend({
   actions: {
      foo() { ... }
   }
});

and another component which inherits from it:

app/components/b/component.js

import A from 'components/a';

export default EmberComponent.extend(A, {
  ...
});

How do I override foo in B? Defining my own actions object does not appear to work.