.net - Find Exact ASP.NET Type Of Page From Inside A Master Page?

I'm trying to retrieve a custom Attribute set on a page's class from inside the MasterPage. Normally to do this I would need to reflect directly on the specific class, but inside the Master page it's always referred to as the Page type (the parent class). How do I determine the specific type of the Page property?

Here's an example of what I'm trying to do:
Dim attrs() As Object = Page.GetType().GetCustomAttributes(GetType(MyCustomAttribute), False)
For Each attr As MyCustomAttribute In attrs
' Do something '
Next

but it only ever returns the attributes attached to the actual Page class.

I'd rather not have to derive a new base type from Page if I can avoid it.

Here is how my class is defined (in the code-behind):<MyCustom()> _Partial Class PageClass Am I defining this in the wrong place?