diff --git a/include/boost/system/detail/error_category_impl.hpp b/include/boost/system/detail/error_category_impl.hpp
index af2185a..252f845 100644
--- a/include/boost/system/detail/error_category_impl.hpp
+++ b/include/boost/system/detail/error_category_impl.hpp
@@ -92,4 +92,17 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
 
 } // namespace boost
 
+// interoperability with std::error_code, std::error_condition
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+#include <boost/system/detail/std_interoperability.hpp>
+
+inline boost::system::error_category::operator std::error_category const & () const
+{
+    return boost::system::detail::to_std_category( *this );
+}
+
+#endif // #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
 #endif // #ifndef BOOST_SYSTEM_DETAIL_ERROR_CATEGORY_IMPL_HPP_INCLUDED
diff --git a/include/boost/system/error_code.hpp b/include/boost/system/error_code.hpp
index de95b13..5ef7ae5 100644
--- a/include/boost/system/error_code.hpp
+++ b/include/boost/system/error_code.hpp
@@ -140,17 +140,4 @@ inline char const * boost::system::detail::system_error_category::message( int e
 
 #endif // #if defined(BOOST_WINDOWS_API)
 
-// interoperability with std::error_code, std::error_condition
-
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
-#include <boost/system/detail/std_interoperability.hpp>
-
-inline boost::system::error_category::operator std::error_category const & () const
-{
-    return boost::system::detail::to_std_category( *this );
-}
-
-#endif // #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
 #endif // BOOST_SYSTEM_ERROR_CODE_HPP_INCLUDED