Fixes #29698

Change-Id: I0531c0a274b120af8871aa2f5975744ff6c912a3
Reviewed-on: https://go-review.googlesource.com/c/157638
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>