Fixes #21105

Change-Id: Ia2dea9b82a356795f581ce75616198b46e97abb6
Reviewed-on: https://go-review.googlesource.com/75253
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>