Различия между boost::enable_if и std::enable_if

#include <cstdint>
#include <type_traits>
//-------------------------------------------------------------------------
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_fundamental.hpp>
//-------------------------------------------------------------------------
template <typename T, typename Predicate = void> struct BoostTest;
template <typename T> struct BoostTest <T, typename boost::enable_if<boost::is_integral<T>>::type> { };
//-------------------------------------------------------------------------
template <typename T, typename Predicate = void> struct StdTest;
template <typename T> struct StdTest <T, typename std::enable_if<std::is_integral<T>::value_type>::type> { };
//-------------------------------------------------------------------------
int main(int argc, char** argv)
{
  StdTest<int> stdOk;       // Err???
  StdTest<float> stdErr;    // Err
  BoostTest<int> boostOk;   // Ok
  BoostTest<float> boostErr;// Err
  return 0;
}