clear a WaitHandle?

I have a file watcher notifying me when a file changes:

static AutoResetEvent InputEvt = new AutoResetEvent(false);

private void fileSystemWatcher1_Changed(object sender, FileSystemEventArgs e)
{
  .
  .
  InputEvt.Set();
}

private bool ReadReply(int timeoutSeconds)
{
  int milliseconds = timeoutSeconds * 1000;
  WaitHandle[] syncobjects = new WaitHandle[1] { abcInputEvt };
  int index = WaitHandle.WaitAny(syncobjects, milliseconds);
  .
  .
}

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Problem is my ReadReply returns immediately instead of waiting for the file to change or the timeout to expire.

I can only guess that my file watcher fired once before, awhile ago, before I became interested in watching for a file change, and that previous change has already set InputEvt to true.

Is there a way I can reset InputEvt before waiting on it? Or is there a way I can test InputEvt to see if it is set or not, to see if that is indeed the problem?