Fixes #11290.

Change-Id: I312f0731077b78a4bed47062eb7fd1ab52bc3dd1
Reviewed-on: https://go-review.googlesource.com/17453Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>