Fixes #21526

Change-Id: I2f8215cd671641cddfa8499f8a8c0130db93dbc6
Reviewed-on: https://go-review.googlesource.com/c/go/+/61291Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>