stampit: Cannot create a stamp from an ES6 class

import stampit from 'stampit';
import test from 'tape';

test('stamp from ES6 class', (t) => {
  t.plan(1);

  class Foo {}
  const fooStamp = stampit.convertConstructor(Foo);

  t.ok(
    fooStamp(),
    'should create instance'
  );
});

TypeError: Cannot call a class as a function