Is it valid to use Object.defineProperties with symbols?

Let's take the following code:

var obj = {};
var x = Symbol();
Object.defineProperties(obj, {
  [x]: {
    value: true,
    writable: true
  },
  "property2": {
    value: "Hello",
    writable: false
  }
  // etc. etc.
});
console.log(obj[x])

Is this valid?

With the native Object.defineproperties code we get in the console.log true.

With the polyfill of zone.js

which is of the form of :

  Object.defineProperties = function (obj, props) {
    Object.keys(props).forEach(function (prop) {
      Object.defineProperty(obj, prop, props[prop]);
    });
    return obj;
  };

we get for the same code of console.log undefined.

This is because of the Object.keys function. I googled around and did not find in any place if this should be allowed or not.