Enabling directory listings with Apache on Lion Server?

I’m running Lion Server with the Web and Wiki enabled. The web site displays OK. But if the URL refers to a directory with no index.html file I don’t get a directory listing even though I’ve modified the apache config file to enable them. Now I may have made a mistake in the config. But what’s odd is that instead of a directory listing I get the main Wiki home page. It looks like whenever the URL resolves to a directory that exists, but which contains no index.html file, the system displays the Wiki page. But I haven’t figured out where this is configured, whether this is the expected behaviour, and if so how I’m supposed to enable directory listings in such cases. Any suggestions?