Fixes #17551.

Change-Id: I84b7d82654cda3559c119aa56b07f30d0d224865
Reviewed-on: https://go-review.googlesource.com/31857
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>