Fixes #14740

Change-Id: Iad8d971c21977b0a1f4ef55a08bb180a8125e976
Reviewed-on: https://go-review.googlesource.com/20562Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>