Fixes #12078

Change-Id: If09c927fae639ec4ed3894a2b393a87c1e677803
Reviewed-on: https://go-review.googlesource.com/16829
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>