Fixes #14050.

Change-Id: I2d9c32213b0da35703edf28f92ed3efb23325921
Reviewed-on: https://go-review.googlesource.com/18792
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>