Fixes #18283

Change-Id: Ic044d2d0657579e8e7786d7264fda2037ddc5ffb
Reviewed-on: https://go-review.googlesource.com/34280
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>