Last play of the game, 4th down, inadvertant whistle

[futurecoach]

Hi everyone. I am taking an Officiating class for my degree requirements to be a coach we had a question about a situation that I'd like to know how you call it.

Situation:

It is fourth down with 4 seconds left. The ball is snapped and after time runs out the play is blown dead due to an inadvertant whistle. Do you award an untimed down?

I think, according to rule 3-3-3c that you do give an untimed down. The guys in class were saying that since it is 4th down you don't.

What are you supposed to do?