Fixes #21075

Change-Id: Idfe5002dfe17943844d9427e27f82ce894b92e80
Reviewed-on: https://go-review.googlesource.com/50270Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>