Setting up multiple domains for single app_id

Facebook recently added the option for multiple domain support within an app. You can find the post here:

https://de开发者_开发知识库velopers.facebook.com/blog/post/570/

However, when I add the second domain to the app_domain, I get the following error:

Error siteB.org must be derived from your Site URL.

My site URL is: fb.siteA.com

Can you add additional site URLs that are comma delimited? e.g. fb.siteA.com, www.siteB.org

Thoughts? What needs to be adjusted?