Fixes #18319

Change-Id: If88e60a86828f60d8d93fc291932c19bab19e8dc
Reviewed-on: https://go-review.googlesource.com/34470Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>