--- a/boost/concept_check.hpp
+++ b/boost/concept_check.hpp
@@ -136,20 +136,21 @@ namespace boost
   {
     BOOST_CONCEPT_USAGE(Assignable) {
 #if !defined(_ITERATOR_) // back_insert_iterator broken for VC++ STL
-      a = a;             // require assignment operator
+      a = b;             // require assignment operator
 #endif
-      const_constraints(a);
+      const_constraints(b);
     }
    private:
-    void const_constraints(const TT& b) {
+    void const_constraints(const TT& x) {
 #if !defined(_ITERATOR_) // back_insert_iterator broken for VC++ STL
-      a = b;              // const required for argument to assignment
+      a = x;              // const required for argument to assignment
 #else
-      ignore_unused_variable_warning(b);
+      ignore_unused_variable_warning(x);
 #endif
     }
    private:
     TT a;
+    TT b;
   };
 
   
@@ -180,22 +181,23 @@ namespace boost
   BOOST_concept(SGIAssignable,(TT))
   {
     BOOST_CONCEPT_USAGE(SGIAssignable) {
-      TT b(a);
+      TT c(a);
 #if !defined(_ITERATOR_) // back_insert_iterator broken for VC++ STL
-      a = a;              // require assignment operator
+      a = b;              // require assignment operator
 #endif
-      const_constraints(a);
-      ignore_unused_variable_warning(b);
+      const_constraints(b);
+      ignore_unused_variable_warning(c);
     }
    private:
-    void const_constraints(const TT& b) {
-      TT c(b);
+    void const_constraints(const TT& x) {
+      TT c(x);
 #if !defined(_ITERATOR_) // back_insert_iterator broken for VC++ STL
-      a = b;              // const required for argument to assignment
+      a = x;              // const required for argument to assignment
 #endif
       ignore_unused_variable_warning(c);
     }
     TT a;
+    TT b;
   };
 #if (defined _MSC_VER)
 # pragma warning( pop )