Onboard fails to start; missing Atspi

$ onboard
Traceback (most recent call last):
  File "/usr/bin/onboard", line 35, in <module>
    from Onboard.OnboardGtk import OnboardGtk as Onboard
  File "/usr/lib/python3/dist-packages/Onboard/OnboardGtk.py", line 35, in <module>
    require_gi_versions()
  File "/usr/lib/python3/dist-packages/Onboard/Version.py", line 28, in require_gi_versions
    gi.require_version('Atspi', '2.0')
  File "/usr/lib/python3/dist-packages/gi/__init__.py", line 102, in require_version
    raise ValueError('Namespace %s not available' % namespace)
ValueError: Namespace Atspi not available

It looks like onboard should have a dependency on python3-atspi, but it does not.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: onboard 1.2.0-0ubuntu5
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat May 21 09:18:07 2016
InstallationDate: Installed on 2016-05-07 (14 days ago)
InstallationMedia: Xubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: onboard
UpgradeStatus: Upgraded to xenial on 2016-05-07 (13 days ago)