diff --git a/include/boost/concept/detail/concept_def.hpp b/include/boost/concept/detail/concept_def.hpp
index 56ba817..c8949c2 100755
--- a/include/boost/concept/detail/concept_def.hpp
+++ b/include/boost/concept/detail/concept_def.hpp
@@ -3,9 +3,10 @@
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 #ifndef BOOST_CONCEPT_DETAIL_CONCEPT_DEF_DWA200651_HPP
 # define BOOST_CONCEPT_DETAIL_CONCEPT_DEF_DWA200651_HPP
-# include <boost/preprocessor/comma_if.hpp>
 # include <boost/preprocessor/seq/for_each_i.hpp>
 # include <boost/preprocessor/seq/enum.hpp>
+# include <boost/preprocessor/comma_if.hpp>
+# include <boost/preprocessor/cat.hpp>
 #endif // BOOST_CONCEPT_DETAIL_CONCEPT_DEF_DWA200651_HPP
 
 // BOOST_concept(SomeName, (p1)(p2)...(pN))
@@ -14,16 +15,21 @@
 //
 // Also defines an equivalent SomeNameConcept for backward compatibility.
 // Maybe in the next release we can kill off the "Concept" suffix for good.
+# define BOOST_concept(name, params)                                            \
+    template < BOOST_PP_SEQ_FOR_EACH_I(BOOST_CONCEPT_typename,~,params) >       \
+    struct name; /* forward decl */                                             \
+                                                                                \
+    template < BOOST_PP_SEQ_FOR_EACH_I(BOOST_CONCEPT_typename,~,params) >       \
+    struct BOOST_PP_CAT(name,Concept)                                           \
+      : name< BOOST_PP_SEQ_ENUM(params) >                                       \
+    {                                                                           \
+        BOOST_PP_CAT(name,Concept)(); /* ctor needed to satisfy gcc-3.4.4 */    \
+    };                                                                          \
+                                                                                \
+    template < BOOST_PP_SEQ_FOR_EACH_I(BOOST_CONCEPT_typename,~,params) >       \
+    struct name                                                                
+    
+// Helper for BOOST_concept, above.
 # define BOOST_CONCEPT_typename(r, ignored, index, t) \
     BOOST_PP_COMMA_IF(index) typename t
 
-# define BOOST_concept(name, params)                                            \
-    template < BOOST_PP_SEQ_FOR_EACH_I(BOOST_CONCEPT_typename, ~, params) >     \
-    struct name;                                                                \
-    template < BOOST_PP_SEQ_FOR_EACH_I(BOOST_CONCEPT_typename, ~, params) >     \
-    struct BOOST_PP_CAT(name,Concept) : name< BOOST_PP_SEQ_ENUM(params) >       \
-    { BOOST_PP_CAT(name,Concept)(); }; /* ctor needed to satisfy gcc-3.4.4 */   \
-    template < BOOST_PP_SEQ_FOR_EACH_I(BOOST_CONCEPT_typename, ~, params) >     \
-    struct name                                                                
-    
-