Can't access property inside a prototype method in JavaScript

Question

Assume the following constructor function:

function MyClass(){
    let myProperty= false;

    Object.defineProperty(this, 'myProperty', {
        get: function(){
            return myProperty
        }
    });
}

I am now trying to access 'myProperty' in a 'start' prototype method:

MyClass.prototype.start = () => {
    console.log('myProperty---> ' + this.myProperty)
}

But this does not work:

let x = new MyClass
//undefined
x.start()
//'myProperty---> 'undefined 
/*myProperty should be false*/

What am I doing wrong? It's almost as if the 'Object.defineProperty' method didn't do it's job of making 'myProperty' public....

(ALL CODE RUNNING IN GOOGLE CHROME CONSOLE)