Use of prototype constructor in JS

Can someone explain to me use of Me.prototype.constructor = Me; and why is needed, when this code is working and without it?

In code prototype object is created on Me object and it is instantiated and replaced old prototype object. Why do I need to point to Me constructor in a given up code?

function Me(){
    this.name = 'Dejan';

}

function You(){
    this.name = 'Ivan';
}

Me.prototype = new You();

somebody = new Me();

Me.prototype.constructor = Me; // Why?

Me.prototype.foo = function(){
    alert('Proto Me!'); // It always fire up this alert, ether constructor is pointing to Me or not... !
}

You.prototype.foo = function(){
    alert('Proto You!');
}

somebody.foo();
alert(somebody.name); // Alert 'Dejan'