Sinon function stubbing: How to call "own" function inside module

I am writing some unit tests for node.js code and I use Sinon to stub function calls via

var myFunction = sinon.stub(nodeModule, 'myFunction');
myFunction.returns('mock answer');

The nodeModule would look like this

module.exports = {
  myFunction: myFunction,
  anotherF: anotherF
}

function myFunction() {

}

function anotherF() {
  myFunction();
}

Mocking works obviously for use cases like nodeModule.myFunction(), but I am wondering how can I mock the myFunction() call inside anotherF() when called with nodeModule.anotherF()?