diff --git a/include/boost/system/detail/error_category.hpp b/include/boost/system/detail/error_category.hpp
index 2226678..5aa0c38 100644
--- a/include/boost/system/detail/error_category.hpp
+++ b/include/boost/system/detail/error_category.hpp
@@ -38,6 +38,12 @@ namespace detail
 
 BOOST_SYSTEM_CONSTEXPR bool failed_impl( int ev, error_category const & cat );
 
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+std::error_category const & to_std_category( error_category const & cat );
+
+#endif
+
 } // namespace detail
 
 #if ( defined( BOOST_GCC ) && BOOST_GCC >= 40600 ) || defined( BOOST_CLANG )
@@ -52,6 +58,10 @@ private:
     friend std::size_t hash_value( error_code const & ec );
     friend BOOST_SYSTEM_CONSTEXPR bool detail::failed_impl( int ev, error_category const & cat );
 
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+    friend std::error_category const & detail::to_std_category( error_category const & cat );
+#endif
+
 #if !defined(BOOST_NO_CXX11_DELETED_FUNCTIONS)
 public:
 
diff --git a/include/boost/system/detail/error_category_impl.hpp b/include/boost/system/detail/error_category_impl.hpp
index 252f845..35cba4b 100644
--- a/include/boost/system/detail/error_category_impl.hpp
+++ b/include/boost/system/detail/error_category_impl.hpp
@@ -96,7 +96,7 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
-#include <boost/system/detail/std_interoperability.hpp>
+#include <boost/system/detail/to_std_category.hpp>
 
 inline boost::system::error_category::operator std::error_category const & () const
 {
diff --git a/include/boost/system/detail/std_interoperability.hpp b/include/boost/system/detail/to_std_category.hpp
similarity index 90%
rename from include/boost/system/detail/std_interoperability.hpp
rename to include/boost/system/detail/to_std_category.hpp
index 66ebecb..3151f5c 100644
--- a/include/boost/system/detail/std_interoperability.hpp
+++ b/include/boost/system/detail/to_std_category.hpp
@@ -1,3 +1,6 @@
+#ifndef BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
+
 // Support for interoperability between Boost.System and <system_error>
 //
 // Copyright 2018 Peter Dimov
@@ -7,6 +10,10 @@
 //
 // See library home page at http://www.boost.org/libs/system
 
+#include <boost/system/detail/error_category.hpp>
+#include <boost/system/detail/error_condition.hpp>
+#include <boost/system/detail/error_code.hpp>
+#include <boost/system/detail/generic_category.hpp>
 #include <system_error>
 #include <map>
 #include <memory>
@@ -80,12 +87,12 @@ struct cat_ptr_less
 
 inline std::error_category const & to_std_category( boost::system::error_category const & cat )
 {
-    if( cat == boost::system::system_category() )
+    if( cat.id_ == boost::system::detail::system_category_id )
     {
         static const std_category system_instance( &cat, 0x1F4D7 );
         return system_instance;
     }
-    else if( cat == boost::system::generic_category() )
+    else if( cat.id_ == boost::system::detail::generic_category_id )
     {
         static const std_category generic_instance( &cat, 0x1F4D3 );
         return generic_instance;
@@ -180,3 +187,5 @@ inline bool std_category::equivalent( const std::error_code & code, int conditio
 } // namespace system
 
 } // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED