Fixes #17697.

Change-Id: I3c47e139b09bde81566e29a1ac0ec8c58d55a34a
Reviewed-on: https://go-review.googlesource.com/32539
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>