Fixes #22904.

Change-Id: Id504504eda7275c10d3c665add8b7ccd23f65820
Reviewed-on: https://go-review.googlesource.com/80301
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>