Having trouble protecting single URLs with membership plugin.

I'm able to protect children of a parent url with no problem using regular expressions, but I'm having trouble protecting that parent url.

For example, let's say I have a parent URL:
http://example.com/parent-page/

And a child of that parent:
http://example.com/parent-page/child-page1

I'm able to protect the child page in URL groups with this:
http://example.com/parent-page/(.*)

But this doesn't seem to protect the parent page itself, nor does simply writing the actual parent url without a regular expression.

What am I doing wrong?