Fixes #16299.

Change-Id: I76f541c7f11edb625df566f2f1035147b8bcd9dd
Reviewed-on: https://go-review.googlesource.com/24830
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>