Fixes #16378.

Change-Id: I99a064f1afec78fb63cb3719061d20be0f21d45d
Reviewed-on: https://go-review.googlesource.com/24930
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>