Fixes golang/go#25341

Change-Id: I79cb4c77b771e005eb27d4e495ac6a7491e2e66e
Reviewed-on: https://go-review.googlesource.com/112696
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>