Fixes #13346.

Change-Id: Ic903ee90575e8dbe23905d0678d3295745d1d47f
Reviewed-on: https://go-review.googlesource.com/18154
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>