Fixes #10010.

Change-Id: Ib13ac28eafed72c456d8b5b6549015cdf5fdda94
Reviewed-on: https://go-review.googlesource.com/56190Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>