Error c2248 when exporting a class that has a private member of type std::stack

Why do I get this error:

Error   2   error C2248: 'std::unique_ptr<_Ty>::unique_ptr' : cannot access private member declared in class 'std::unique_ptr<_Ty>' c:\program files (x86)\microsoft visual studio 11.0\vc\include\xmemory0 606 1   UNIQUE_PTR

when trying to Export this class with __declspec(dllexport)?

class __declspec(dllexport) A
{
private:
    std::stack<std::unique_ptr<int>> ints;
};

Im using vs2012