Fixes #20749.

Change-Id: Ic6a7edc858575c4cb8b2e2ca97ee0c4b69f22c27
Reviewed-on: https://go-review.googlesource.com/46466
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>