Attached patch fixes the issue, but it has no unit test :-(

On Windows, it looks like IocpProactor can also raise an error if the timeout is too large:

            # GetQueuedCompletionStatus() has a resolution of 1 millisecond,
            # round away from zero to wait *at least* timeout seconds.
            ms = math.ceil(timeout * 1e3)
            if ms >= INFINITE:
                raise ValueError("timeout too big")

with INFINITE = 0xffffffff.