Fixes #15124

Change-Id: I55fe4c2957370f3fb417c3df54f99fb085a5dada
Reviewed-on: https://go-review.googlesource.com/21522Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>