default contruct a unique_ptr with a deleter

I have code that fails when I construct a unique_ptr with a deleter. Here's a replica of my code.

// defined in a C library
struct A;
A* make_A();
void delete_A(A*);

// C++
struct myStruct{
std::unique_ptr<A,void(*)(A*)> pA; // I want to assign it later (using move)
}

error:

error: static assertion failed: constructed with null function pointer deleter

I can't see what is wrong...

Note: gcc version 4.7.2 (Debian 4.7.2)