Fixes #20315

Change-Id: I5d5c82f10902b59168fc0cca0af50286843df55d
Reviewed-on: https://go-review.googlesource.com/82375
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>