c++ - incomplete type / forward declaration

This question has been asked many times but usually it could be easily solved by changing order of classes. In my case it may be not.

class GCRefLink;
class GCRef;

class GCRefLink {
  friend class GCRef;
private:
  GCRef * ref;
  GCRefLink(GCRef * ref) : ref(ref) {}
public:
  ~GCRefLink(){this->ref->unlink();}
};

class GCRef {
 friend class GCRefLink;
private:
  int refCount;

  GCRef() : refCount(0) {}
  virtual ~GCRef(){}

  void unlink(){--this->refCount;if(this->refCount==0) delete this;}
public:
  GCRefLink link(){++this->refCount;return GCRefLink(this);}
};

When I change order of classes I'm getting the same error just about second class. It's meant to be reference class to inherit by managed, undeleteable classes, I know there's already such a thing in stl but as it's university project I need to implement my own.

I'm getting invalid use of incomplete type 'class GCRef' or invalid use of incomplete type 'class GCRefLink' errors