Fixes #19576.

Change-Id: I11034fb08e989f6eb7d54bde873b92804223598d
Reviewed-on: https://go-review.googlesource.com/38291
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>