Overloading global swap for user-defined type

Question

The C++ standard prohibits declaring types or defining anything in namespace std, but it does allow you to specialize standard STL templates for user-defined types.

Usually, when I want to specialize std::swap for my own custom templated type, I just do:

namespace std
{
  template <class T>
  void swap(MyType<T>& t1, MyType<T>& t2)
  {
     t1.swap(t2);
  }
}

...and that works out fine. But I'm not entirely sure if my usual practice is standard compliant. Am I doing this correctly?