Fixes #9236

Change-Id: I744d7f071e945ea6e6e50203d931f4678c8b545d
Reviewed-on: https://go-review.googlesource.com/17311Reviewed-by: Adam Langley <agl@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>