diff --git a/boost/mpl/aux_/na_fwd.hpp b/boost/mpl/aux_/na_fwd.hpp
new file mode 100644
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--- /dev/null
+++ b/boost/mpl/aux_/na_fwd.hpp
@@ -0,0 +1,31 @@
+
+#ifndef BOOST_MPL_AUX_NA_FWD_HPP_INCLUDED
+#define BOOST_MPL_AUX_NA_FWD_HPP_INCLUDED
+
+// Copyright Aleksey Gurtovoy 2001-2004
+//
+// 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)
+//
+// See http://www.boost.org/libs/mpl for documentation.
+
+// $Id: na_fwd.hpp 49267 2008-10-11 06:19:02Z agurtovoy $
+// $Date: 2008-10-10 23:19:02 -0700 (Fri, 10 Oct 2008) $
+// $Revision: 49267 $
+
+#include <boost/mpl/aux_/adl_barrier.hpp>
+
+BOOST_MPL_AUX_ADL_BARRIER_NAMESPACE_OPEN
+
+// n.a. == not available
+struct na
+{
+    typedef na type;
+    enum { value = 0 };
+};
+
+BOOST_MPL_AUX_ADL_BARRIER_NAMESPACE_CLOSE
+BOOST_MPL_AUX_ADL_BARRIER_DECL(na)
+
+#endif // BOOST_MPL_AUX_NA_FWD_HPP_INCLUDED