unrecognized properties on this 'this' in mongoose virtuals with typegoose

Question

I'm trying to define a virtual property on a typegoose model.

class foo {
  ...
  start: Date
  end: Date
  get duration(){
    return this.end - this.start
  }
}

I get typescript errors that this doesn't have the properties end or start. Is there a way to make it work properly?

Thanks