friend classes?

[wey97]

How in the hell can you use two classes inside each other in the
same file?
I could have sworn this used to work:

class cl1
{
	public:
	int i;
	cl1(cl2 c2){i = c2.i;}
	friend class cl2;
};

// error: missing ')' before identifier c2

class cl2
{
	public:
	int i;
	cl2(cl1 c1){i = c1.i;}
	friend class cl1;
};

// this is fine