boost.variant derived type: cannot use copy constructor

I have a type that derives from boost::variant<T, E>. I do the following, and I cannot use the copy constructor, I cannot figure out why, some SFINAE seems to fail. Looks that the boost::variant<T, E> construction is swallowing a T as ExpectedResult<T, E> in the inherited constructor. How could I fix it to make it work and with the simplest solution?

template <class T, class E>
class ExpectedResult : boost::variant<T, E> {
public:
    using boost::variant<T, E>::variant;
};

ExpectedResult<int,float> er;
ExpectedResult<int, float> er2 = er;


error: no type named 'type' in 'boost::enable_if<boost::mpl::and_<boost::mpl::not_<boost::is_same<Emotiv::Cortex::Utilities::ExpectedResult<int, float>, boost::variant<int, float> > >, boost::detail::variant::is_variant_constructible_from<const Emotiv::Cortex::Utilities::ExpectedResult<int, float> &, boost::mpl::l_item<mpl_::long_<2>, int, boost::mpl::l_item<mpl_::long_<1>, float, boost::mpl::l_end> > >, mpl_::bool_<true>, mpl_::bool_<true>, mpl_::bool_<true> >, void>'; 'enable_if' cannot be used to disable this declaration
        typename boost::enable_if<mpl::and_<
                                  ^~~~~~~~~~
note: in instantiation of member function 'boost::variant<int, float>::variant' requested here
    using boost::variant<T, E>::variant;
    while substituting deduced template arguments into function template 'ExpectedResult' [with T = Emotiv::Cortex::Utilities::ExpectedResult<int, float>]
    ExpectedResult<int, float> er2 = er;