Derived Classes and namespaces

Question

I am deriving a class, for use in my application, from a class provided by another group. Should the derived class be in the namespace for my application or the namespace of the parent class?

While I am extending the class to add features I need, the added features are not specific to my application. The project that contains the parent class is also rarely updated so there is a chance my additions would never be picked up... Maybe none of this matters.