Fixes #13263.

Change-Id: Ie1cafc62b6bfe6c5381c35d9a95563267b4cc9b0
Reviewed-on: https://go-review.googlesource.com/33970Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>