CRTP can't see structs define in derived class

Question

I am getting some behavior I don't understand when experimenting with CRTP.

template<class This>
struct Base
{
    typename This::Event getEvent() { return {}; }
};

struct Derived : Base<Derived>
{
    struct Event { };
};

int main()
{
    auto x = Derived();
    auto event = x.getEvent();
}

I am getting the error

sketch2.cpp:5:24: error: no type named 'Event' in 'Derived'
        typename This::Event getEvent() { return {}; }
        ~~~~~~~~~~~~~~~^~~~~

But it should resolve to Derived::Event, which is well-defined, is it not? Is it possible to have methods of a base class depend on types defined in the derived class like this?