Fixes #17231

Change-Id: I0d6007ab504f2277cb6affc9e2050157a6ad4d5e
Reviewed-on: https://go-review.googlesource.com/29970Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>