Fixes #9634.

Change-Id: I7b18f26c2fb812978fc7adc5bfd39ebfffe48701
Reviewed-on: https://go-review.googlesource.com/3080Reviewed-by: Minux Ma <minux@golang.org>
(cherry picked from commit f5b8813e)
Reviewed-on: https://go-review.googlesource.com/5000
Run-TryBot: Andrew Gerrand <adg@golang.org>