Fixes #16303.

Change-Id: I2832477ce0117a66da53ca1f198ebb6121953d56
Reviewed-on: https://go-review.googlesource.com/24833
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>