Decorator Pattern with generics in Flow (not working)

DecoratorPattern.js

// @flow

class SuperClass {
    something () {
    }
}

class SubClass extends SuperClass {
}

function decorateWithSomethingElse <T: Class<SuperClass>> (SuperClass: T): T {
    return class SomethingElseAdded extends SuperClass {
        addSomethingElse () {
        }
    }
}

var SubClassWithSomethingElse = decorateWithSomethingElse(SubClass)

// (new SubClass) instanceof SuperClass -> true
// (new SubClassWithSomethingElse) instanceof SubClass -> true
// (new SubClassWithSomethingElse) instanceof SuperClass -> true