Fixes #18092.

Change-Id: I54e2da2e0f168c068f5e4a1b22ba508d78259168
Reviewed-on: https://go-review.googlesource.com/33658
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>