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diff --git a/boost/convert/detail/boost_parameter_ext.hpp b/boost/convert/detail/boost_parameter_ext.hpp
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+++ b/boost/convert/detail/boost_parameter_ext.hpp
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+// Copyright (c) 2009-2014 Vladimir Batov.
+// Use, modification and distribution are subject to the Boost Software License,
+// Version 1.0. See http://www.boost.org/LICENSE_1_0.txt.
+
+#ifndef BOOST_PARAMETER_EXT_PRIVATE_HPP
+#define BOOST_PARAMETER_EXT_PRIVATE_HPP
+
+#include <boost/parameter/keyword.hpp>
+
+// A Boost.Parameter extension by Andrey Semashev.
+// This should really go to Boost.Parameter in the end.
+
+namespace boost { namespace parameter {
+
+// The metafunction, given the type of the arguments pack and the keyword tag,
+// returns the corresponding parameter type
+template< typename ArgsT, typename KeywordTagT >
+struct parameter_type
+{
+    typedef void type;
+};
+
+template< typename ArgT, typename KeywordTagT >
+struct parameter_type<aux::tagged_argument<KeywordTagT, ArgT>, KeywordTagT>
+{
+    typedef typename aux::tagged_argument< KeywordTagT, ArgT >::value_type type;
+};
+
+template< typename KeywordTagT1, typename ArgT, typename KeywordTagT2 >
+struct parameter_type< aux::tagged_argument< KeywordTagT1, ArgT >, KeywordTagT2 >
+{
+    typedef void type;
+};
+
+template< typename ArgT, typename TailT, typename KeywordTagT >
+struct parameter_type<
+    aux::arg_list<
+        aux::tagged_argument< KeywordTagT, ArgT >,
+        TailT
+    >,
+    KeywordTagT
+>
+{
+    typedef typename aux::tagged_argument< KeywordTagT, ArgT >::value_type type;
+};
+
+template< typename KeywordTagT1, typename ArgT, typename TailT, typename KeywordTagT2 >
+struct parameter_type<
+    aux::arg_list<
+        aux::tagged_argument< KeywordTagT1, ArgT >,
+        TailT
+    >,
+    KeywordTagT2
+> :
+    public parameter_type< TailT, KeywordTagT2 >
+{
+};
+
+}} // boost::parameter
+
+#endif // BOOST_PARAMETER_EXT_PRIVATE_HPP
+