bzr-gtk - running 'bzr visualize' as sudo root crashes with 'internal error'

Ii expect a nice errormessage like 'DISPLAY not set' but I get this:

chris@chris:~$ sudo su -

root@chris:~# bzr visualize

/var/lib/python-support/python2.5/gtk-2.0/gtk/__init__.py:72: GtkWarning: could not open display
  warnings.warn(str(e), _gtk.Warning)
/usr/lib/python2.5/site-packages/bzrlib/plugins/gtk/window.py:8: Warning: invalid (NULL) pointer instance
  gtk.Window.__init__(self, gtk.WINDOW_TOPLEVEL)
/usr/lib/python2.5/site-packages/bzrlib/plugins/gtk/window.py:8: Warning: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed
  gtk.Window.__init__(self, gtk.WINDOW_TOPLEVEL)
bzr: ERROR: exceptions.AttributeError: 'NoneType' object has no attribute 'get_monitor_geometry'

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 727, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 922, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 559, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.5/site-packages/bzrlib/plugins/gtk/__init__.py", line 288, in run
    pp = start_viz_window(br, revids, limit)
  File "/usr/lib/python2.5/site-packages/bzrlib/plugins/gtk/__init__.py", line 257, in start_viz_window
    return BranchWindow(branch, revisions, limit)
  File "/usr/lib/python2.5/site-packages/bzrlib/plugins/gtk/viz/branchwin.py", line 67, in __init__
    monitor = screen.get_monitor_geometry(0)
AttributeError: 'NoneType' object has no attribute 'get_monitor_geometry'

bzr 1.14.1 on python 2.5.2 (linux2)
arguments: ['/usr/bin/bzr', 'visualize']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'
plugins:
  bzrtools /usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [1.14]
  cvsps_import /usr/lib/python2.5/site-packages/bzrlib/plugins/cvsps_import [unknown]
  gtk /usr/lib/python2.5/site-packages/bzrlib/plugins/gtk [0.95.0.final.1]
  launchpad /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  netrc_credential_store /usr/lib/python2.5/site-packages/bzrlib/plugins/netrc_credential_store [unknown]
  rebase /usr/lib/python2.5/site-packages/bzrlib/plugins/rebase [0.3]
  svn /usr/lib/python2.5/site-packages/bzrlib/plugins/svn [0.5.4]
  upload /usr/lib/python2.5/site-packages/bzrlib/plugins/upload [0.1]
  xmloutput /usr/lib/python2.5/site-packages/bzrlib/plugins/xmloutput [0.8.3]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.