Fixes #7501

Change-Id: Iac7c79cd4b30a90b14ed84bf1eba758972232a6c
Reviewed-on: https://go-review.googlesource.com/c/go/+/171337
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>