TypeError raised due to tab_width setting in config

Overriding the tab_width setting via a config file is
causing a TypeError in statemachine.py:

$ cat test.ini
[restructuredtext parser]
tab_width = 4

$ rst2html --traceback --config=test.ini test.rst test.html
Traceback (most recent call last):
File "/usr/bin/rst2html", line 25, in ?
publish_cmdline(writer_name='html',
description=description)
File "/usr/lib/site-python/docutils/core.py", line
309, in publish_cmdline
config_section=config_section,
enable_exit_status=enable_exit_status)
File "/usr/lib/site-python/docutils/core.py", line
194, in publish
self.settings)
File
"/usr/lib/site-python/docutils/readers/__init__.py",
line 66, in read
self.parse()
File
"/usr/lib/site-python/docutils/readers/__init__.py",
line 72, in parse
self.parser.parse(self.input, document)
File
"/usr/lib/site-python/docutils/parsers/rst/__init__.py",
line 138, in parse
convert_whitespace=1)
File "/usr/lib/site-python/docutils/statemachine.py",
line 1449, in string2lines
return [s.expandtabs(tab_width) for s in
astring.splitlines()]
TypeError: an integer is required