Fixes #29748

Change-Id: I2b19165bdb3c99df5b79574390b5d5f6d40462dc
Reviewed-on: https://go-review.googlesource.com/c/157961
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>