Can't use with ES6 classes?

I’m trying to use Formsy like so:

import React, {Component} from 'react';
import Formsy from 'formsy-react';
import reactMixin from 'react-mixin';

export default class TestInput extends Component {
  changeValue(event) {
    this.setValue(event.target.value);
  }

  render() {
    return <div>
      <input
        type="text"
        onChange={this.changeValue.bind(this)}
        value={this.getValue()}
      />
    </div>
  }
}

reactMixin(TestInput.prototype, Formsy.Mixin);

And I’m getting this error, along with a couple other similar ones:

Warning: getInitialState was defined on TestInput, a plain JavaScript class. This is only supported for classes created using React.createClass. Did you mean to define a state property instead?

Do I simply have to use React.createClass?

[FutureKode]

For use with es6 I think you can use this https://github.com/christianalfoni/formsy-react/blob/master/API.md#formsyhoc

[simondell]

@apuntovanini Thanks!