Fixes #18003.

Change-Id: Iadcc5c424c64badecfb5fdbd4dbd9197df56182c
Reviewed-on: https://go-review.googlesource.com/33421
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>