Fixes #10912

Change-Id: If04e3205d5cc43ebfd6864bc59340c8697cbc0af
Reviewed-on: https://go-review.googlesource.com/17592
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>