diff --git a/include/boost/multiprecision/detail/number_base.hpp b/include/boost/multiprecision/detail/number_base.hpp
index 1c1267df..0d7fe45a 100644
--- a/include/boost/multiprecision/detail/number_base.hpp
+++ b/include/boost/multiprecision/detail/number_base.hpp
@@ -76,7 +76,7 @@ struct has_enough_bits
 template <class Val, class Backend, class Tag>
 struct canonical_imp
 {
-   typedef typename decay<Val>::type type;
+   typedef typename remove_cv<typename decay<const Val>::type>::type type;
 };
 template <class Val, class Backend>
 struct canonical_imp<Val, Backend, mpl::int_<0> >
diff --git a/include/boost/multiprecision/mpfr.hpp b/include/boost/multiprecision/mpfr.hpp
index 98fa9334..cdbb8cfb 100644
--- a/include/boost/multiprecision/mpfr.hpp
+++ b/include/boost/multiprecision/mpfr.hpp
@@ -1083,7 +1083,6 @@ struct is_explicitly_convertible<backends::mpfr_float_backend<D1>, backends::mpf
 template<>
 struct number_category<typename detail::canonical<mpfr_t, backends::mpfr_float_backend<0> >::type> : public mpl::int_<number_kind_floating_point>{};
 
-
 using boost::multiprecision::backends::mpfr_float_backend;
 
 typedef number<mpfr_float_backend<50> >    mpfr_float_50;
diff --git a/include/boost/multiprecision/number.hpp b/include/boost/multiprecision/number.hpp
index a9ae4721..55b38314 100644
--- a/include/boost/multiprecision/number.hpp
+++ b/include/boost/multiprecision/number.hpp
@@ -1601,7 +1601,11 @@ private:
    template <class B2, bool ET>
    static BOOST_FORCEINLINE BOOST_CONSTEXPR const B2& canonical_value(const number<B2, ET>& v) BOOST_NOEXCEPT {  return v.backend();  }
    template <class V>
-   static BOOST_FORCEINLINE BOOST_CONSTEXPR typename detail::canonical<V, Backend>::type canonical_value(const V& v) BOOST_NOEXCEPT {  return static_cast<typename detail::canonical<V, Backend>::type>(v);  }
+   static BOOST_FORCEINLINE BOOST_CONSTEXPR typename disable_if<is_same<typename detail::canonical<V, Backend>::type, V>, typename detail::canonical<V, Backend>::type>::type 
+      canonical_value(const V& v) BOOST_NOEXCEPT {  return static_cast<typename detail::canonical<V, Backend>::type>(v);  }
+   template <class V>
+   static BOOST_FORCEINLINE BOOST_CONSTEXPR typename enable_if<is_same<typename detail::canonical<V, Backend>::type, V>, const V&>::type 
+      canonical_value(const V& v) BOOST_NOEXCEPT {  return v;  }
    static BOOST_FORCEINLINE typename detail::canonical<std::string, Backend>::type canonical_value(const std::string& v) BOOST_NOEXCEPT {  return v.c_str();  }
 
    static BOOST_FORCEINLINE BOOST_CONSTEXPR const Backend& function_arg_value(const self_type& v) BOOST_NOEXCEPT {  return v.backend();  }
diff --git a/include/boost/multiprecision/rational_adapter.hpp b/include/boost/multiprecision/rational_adapter.hpp
index 5e4ef673..6dd07d6f 100644
--- a/include/boost/multiprecision/rational_adapter.hpp
+++ b/include/boost/multiprecision/rational_adapter.hpp
@@ -41,11 +41,11 @@ struct rational_adapter
    template <class U>
    explicit rational_adapter(const U& u, 
       typename enable_if_c<
-         detail::is_explicitly_convertible<U, IntBackend>::value && !is_convertible<U, IntBackend>::value
+         boost::multiprecision::detail::is_explicitly_convertible<U, IntBackend>::value && !is_convertible<U, IntBackend>::value
       >::type* = 0) 
       : m_value(IntBackend(u)){}
    template <class U>
-   typename enable_if_c<(detail::is_explicitly_convertible<U, IntBackend>::value && !is_arithmetic<U>::value), rational_adapter&>::type operator = (const U& u) 
+   typename enable_if_c<(boost::multiprecision::detail::is_explicitly_convertible<U, IntBackend>::value && !is_arithmetic<U>::value), rational_adapter&>::type operator = (const U& u) 
    {
       m_value = IntBackend(u);
    }