diff --git a/include/boost/fusion/support/unused.hpp b/include/boost/fusion/support/unused.hpp
index 964839ab..1f65015e 100644
--- a/include/boost/fusion/support/unused.hpp
+++ b/include/boost/fusion/support/unused.hpp
@@ -1,5 +1,6 @@
 /*=============================================================================
     Copyright (c) 2001-2011 Joel de Guzman
+    Copyright (c) 2018 Kohei Takahashi
 
     Distributed under the Boost Software License, Version 1.0. (See accompanying
     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -10,7 +11,6 @@
 #include <boost/fusion/support/config.hpp>
 #include <iosfwd>
 
-#include <boost/config.hpp>
 #if defined(BOOST_MSVC)
 # pragma warning(push)
 # pragma warning(disable: 4522) // multiple assignment operators specified warning
@@ -23,9 +23,16 @@ namespace boost { namespace fusion
     struct unused_type
     {
         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        unused_type() BOOST_NOEXCEPT
+        BOOST_DEFAULTED_FUNCTION(
+        unused_type() BOOST_NOEXCEPT,
         {
-        }
+        })
+
+        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+        BOOST_DEFAULTED_FUNCTION(
+        unused_type(unused_type const&) BOOST_NOEXCEPT,
+        {
+        })
 
         template <typename T>
         BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
@@ -33,35 +40,12 @@ namespace boost { namespace fusion
         {
         }
 
-        template <typename T>
-        BOOST_FUSION_CONSTEXPR_THIS BOOST_FUSION_GPU_ENABLED
-        unused_type const&
-        operator=(T const&) const BOOST_NOEXCEPT
-        {
-            return *this;
-        }
-
-        template <typename T>
-        BOOST_CXX14_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        unused_type&
-        operator=(T const&) BOOST_NOEXCEPT
-        {
-            return *this;
-        }
-
         BOOST_FUSION_CONSTEXPR_THIS BOOST_FUSION_GPU_ENABLED
         unused_type const&
         operator=(unused_type const&) const BOOST_NOEXCEPT
         {
             return *this;
         }
-
-        BOOST_CXX14_CONSTEXPR BOOST_FUSION_GPU_ENABLED
-        unused_type&
-        operator=(unused_type const&) BOOST_NOEXCEPT
-        {
-            return *this;
-        }
     };
 
     BOOST_CONSTEXPR_OR_CONST unused_type unused = unused_type();