Fixes #14955.

Change-Id: I157432584bb51088bec565f6bb9e64348345cff9
Reviewed-on: https://go-review.googlesource.com/23571
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>