Fixes #18282

Change-Id: I024ca4a03bbbcccd48a0a6245bc3ec22c6a90288
Reviewed-on: https://go-review.googlesource.com/34254
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
Reviewed-by: Rob Pike <r@golang.org>