diff --git a/cppreg_Defines.h b/cppreg_Defines.h
index acd375e..3d5a254 100644
--- a/cppreg_Defines.h
+++ b/cppreg_Defines.h
@@ -35,25 +35,15 @@ namespace cppreg {
     enum class RegBitSize {
         b8,     //!< 8-bit register.
         b16,    //!< 16-bit register.
-        b32     //!< 32-bit register.
+        b32,    //!< 32-bit register.
+        b64     //!< 64-bit register.
     };
 
-//    //! Type alias for register and field widths.
-//    /**
-//     * This limit the implementation to a maximum size of 256 bits for any
-//     * register or field.
-//     * This corresponds to the number of bits in the a register or field.
-//     */
+    //! Type alias field width.
     using FieldWidth_t = std::uint8_t;
 
 
-    //! Type alias for register and field offsets.
-    /**
-     * This limit the implementation to a maximum offset of 256 bits for any
-     * register or field.
-     * Given that we consider 32 bits address space and 32 bits register this
-     * should be enough.
-     */
+    //! Type alias for field offset.
     using FieldOffset_t = std::uint8_t;
 
 
diff --git a/register/Field.h b/register/Field.h
index d27db10..8b8e391 100644
--- a/register/Field.h
+++ b/register/Field.h
@@ -170,8 +170,8 @@ namespace cppreg {
                                >::type
         write() noexcept {
 
-            // For this particular we can simply forward to the non-constant
-            // implementation.
+            // For this particular we simply forward to the non-constant
+            // implementation because the shadow value needs to be updated.
             write(value);
 
         };
diff --git a/register/MergeWrite.h b/register/MergeWrite.h
index e5f530f..28bd887 100644
--- a/register/MergeWrite.h
+++ b/register/MergeWrite.h
@@ -51,14 +51,11 @@ namespace cppreg {
     > class MergeWrite_tmpl {
 
 
-    public:
-
-        //! Type alias to register base type.
-        using base_type = typename Register::type;
-
-
     private:
 
+        // Type alias to register base type.
+        using base_type = typename Register::type;
+
         // Disabled for shadow value register.
         static_assert(!Register::shadow::value,
                       "merge write is not available for shadow value register");
@@ -135,7 +132,16 @@ namespace cppreg {
             T
                                >::type&&
         with() const && noexcept {
+
+            // Check that the field belongs to the register.
+            static_assert(std::is_same<
+                              typename F::parent_register,
+                              Register
+                                      >::value,
+                          "field is not from the same register in merge_write");
+
             return std::move(T::make());
+
         };
 
 
diff --git a/register/Register.h b/register/Register.h
index 3df39b9..05653e3 100644
--- a/register/Register.h
+++ b/register/Register.h
@@ -25,8 +25,8 @@ namespace cppreg {
     /**
      * @tparam reg_address Register address.
      * @tparam reg_size Register size enum value.
-     * @tparam ResetValue Register reset value (0x0 if unknown).
-     * @tparam UseShadow shadow Boolean flag to enable shadow value.
+     * @tparam reset_value Register reset value (0x0 if unknown).
+     * @tparam use_shadow shadow Boolean flag to enable shadow value.
      *
      * This data structure will act as a container for fields and is
      * therefore limited to a strict minimum. It only carries information
diff --git a/register/RegisterPack.h b/register/RegisterPack.h
index 6325140..b0f269b 100644
--- a/register/RegisterPack.h
+++ b/register/RegisterPack.h
@@ -97,18 +97,18 @@ namespace internals {
     //! Packed register implementation.
     /**
      * @tparam RegisterPack Pack to which the register belongs.
-     * @tparam BitOffset Offset in bits for the register with respect to base.
-     * @tparam RegWidth Register width.
-     * @tparam ResetValue Register reset value (0x0 if unknown).
-     * @tparam UseShadow shadow Boolean flag to enable shadow value.
+     * @tparam reg_size Register size enum value.
+     * @tparam bit_offset Offset in bits for the register with respect to base.
+     * @tparam reset_value Register reset value (0x0 if unknown).
+     * @tparam use_shadow Boolean flag to enable shadow value.
      *
      * This implementation is intended to be used when defining a register
      * that belongs to a peripheral group.
      */
     template <
         typename RegisterPack,
-        std::uint32_t bit_offset,
         RegBitSize reg_size,
+        std::uint32_t bit_offset,
         typename TypeTraits<reg_size>::type reset_value = 0x0,
         bool use_shadow = false
     >
diff --git a/register/ShadowValue.h b/register/ShadowValue.h
index e145787..2725bb9 100644
--- a/register/ShadowValue.h
+++ b/register/ShadowValue.h
@@ -20,11 +20,12 @@ namespace cppreg {
     //! Shadow value generic implementation.
     /**
      * @tparam Register Register type.
-     * @tparam UseShadow Boolean flag indicating if shadow value is required.
+     * @tparam use_shadow Boolean flag indicating if shadow value is required.
      *
      * This implementation is for register which do not require shadow value.
      */
-    template <typename Register, bool UseShadow> struct Shadow : std::false_type {};
+    template <typename Register, bool use_shadow>
+    struct Shadow : std::false_type {};
 
 
     //! Shadow value implementation.
diff --git a/register/Traits.h b/register/Traits.h
index 20870b5..abc1b81 100644
--- a/register/Traits.h
+++ b/register/Traits.h
@@ -19,22 +19,6 @@
 namespace cppreg {
 
 
-//    //! Register data type default implementation.
-//    /**
-//     * @tparam Size Register size.
-//     *
-//     * This will fail to compile if the register size is not implemented.
-//     */
-//    template <Width_t Size>
-//    struct RegisterType;
-//
-//    //!@{ Specializations based on register size.
-//    template <> struct RegisterType<8u> { using type = std::uint8_t; };
-//    template <> struct RegisterType<16u> { using type = std::uint16_t; };
-//    template <> struct RegisterType<32u> { using type = std::uint32_t; };
-//    //!@}
-
-
     //! Register type traits based on size.
     /**
      * @tparam S Register size in bits.
@@ -42,6 +26,9 @@ namespace cppreg {
     template <RegBitSize S>
     struct TypeTraits;
 
+
+    //!@{ TypeTraits specializations.
+    //! 8-bit specialization.
     template <> struct TypeTraits<RegBitSize::b8> {
         using type = std::uint8_t;
         constexpr static const std::uint8_t bit_size = 8u;
@@ -49,6 +36,7 @@ namespace cppreg {
         constexpr static const std::uint8_t max_field_width = 8u;
         constexpr static const std::uint8_t max_field_offset = 8u;
     };
+    //! 16-bit specialization.
     template <> struct TypeTraits<RegBitSize::b16> {
         using type = std::uint16_t;
         constexpr static const std::uint8_t bit_size = 16u;
@@ -56,6 +44,7 @@ namespace cppreg {
         constexpr static const std::uint8_t max_field_width = 16u;
         constexpr static const std::uint8_t max_field_offset = 16u;
     };
+    //! 32-bit specialization.
     template <> struct TypeTraits<RegBitSize::b32> {
         using type = std::uint32_t;
         constexpr static const std::uint8_t bit_size = 32u;
@@ -63,6 +52,15 @@ namespace cppreg {
         constexpr static const std::uint8_t max_field_width = 32u;
         constexpr static const std::uint8_t max_field_offset = 32u;
     };
+    //! 64-bit specialization.
+    template <> struct TypeTraits<RegBitSize::b64> {
+        using type = std::uint64_t;
+        constexpr static const std::uint8_t bit_size = 64u;
+        constexpr static const std::uint8_t byte_size = 8u;
+        constexpr static const std::uint8_t max_field_width = 64u;
+        constexpr static const std::uint8_t max_field_offset = 64u;
+    };
+    //!@}
 
 
 }