Can somebody please explain to me why I'm being stupid? I don't understand why I'm getting this error message:

template <class T> class Base
  {
public:
  int x ;
  } ;

template <class T> class Derived : public Base<T>
  {
public:
  void f() { x = 99 ; } // error: 'x' was not declared in this scope
  } ;

I have to do this to get it to compile:

void f() { Base<T>::x = 99 ; }

I am using g++ version 4.9.1 for MinGW, with std=c++11.