Fixes golang/go#16055.

Change-Id: I80437e2895b0f2bf23e090dec29bd20c2900db9a
Reviewed-on: https://go-review.googlesource.com/24136Reviewed-by: David Anderson <danderson@google.com>
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>