Fixes #29781

Change-Id: Id032d07a54b8c24f0c6d3f6e512932f76920ee04
Reviewed-on: https://go-review.googlesource.com/c/158457
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>