Fixes #17678

Change-Id: I01d12a827e6106efed1ec024f736c640b86906b4
Reviewed-on: https://go-review.googlesource.com/33029
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>