Partial specialization in c++ template : template parameter not deducible

The below code works fine :

template<typename T, int n> 
class Fib {

};

template<typename T,int n>
class Fib<T*,n> {

}; 

But the below code shows error : template parameters not deducible in partial specialization:

 template<typename T, int n> 
 class Fib {

 };

 template<typename T,int n>
 class Fib<T*,0> {

 };

Can you explain the reason for this behaviour ?