struct Foo {
    uint number;

    void doStuff(uint num) {

        void doMoreStuff(T)(T num2) {
            number++;
        }

        doMoreStuff(num);
    }
}

test.d(7): Error: need 'this' to access member number

Also happens if Foo is a class instead of a struct.  Does not happen if doMoreStuff() is a plain old function instead of a function template.