diff --git a/Cartesian_kernel/include/CGAL/Cartesian/Circle_3.h b/Cartesian_kernel/include/CGAL/Cartesian/Circle_3.h
index 9c5d2658657..be0824bc821 100644
--- a/Cartesian_kernel/include/CGAL/Cartesian/Circle_3.h
+++ b/Cartesian_kernel/include/CGAL/Cartesian/Circle_3.h
@@ -81,13 +81,13 @@ public:
     Object obj = R().intersect_3_object()(s1, s2);
     // s1,s2 must intersect
     CGAL_kernel_precondition(!(obj.is_empty()));
-    typename R::Circle_3 circle;
-    typename R::Point_3 point;
-    if(assign(circle, obj))
-      base = Rep(circle.diametral_sphere(), circle.supporting_plane());
+    const typename R::Circle_3* circle_ptr=object_cast<typename R::Circle_3>(&obj);
+    if(circle_ptr!=NULL)
+      base = Rep(circle_ptr->diametral_sphere(), circle_ptr->supporting_plane());
     else {
-      assign(point, obj);
-      CircleC3 circle = CircleC3(point, FT(0), Vector_3(FT(1),FT(0),FT(0)));
+      const typename R::Point_3* point=object_cast<typename R::Point_3>(&obj);
+      CGAL_kernel_precondition(point!=NULL);
+      CircleC3 circle = CircleC3(*point, FT(0), Vector_3(FT(1),FT(0),FT(0)));
       base = Rep(circle.diametral_sphere(), circle.supporting_plane());
     }
   }
@@ -98,13 +98,13 @@ public:
     Object obj = R().intersect_3_object()(p, s);
     // s1,s2 must intersect
     CGAL_kernel_precondition(!(obj.is_empty()));
-    typename R::Circle_3 circle;
-    typename R::Point_3 point;
-    if(assign(circle, obj))
-      base = Rep(circle.diametral_sphere(), circle.supporting_plane());
+    const typename R::Circle_3* circle_ptr=object_cast<typename R::Circle_3>(&obj);
+    if(circle_ptr!=NULL)
+      base = Rep(circle_ptr->diametral_sphere(), circle_ptr->supporting_plane());
     else {
-      assign(point, obj);
-      CircleC3 circle = CircleC3(point, FT(0), Vector_3(FT(1),FT(0),FT(0)));
+      const typename R::Point_3* point=object_cast<typename R::Point_3>(&obj);
+      CGAL_kernel_precondition(point!=NULL);
+      CircleC3 circle = CircleC3(*point, FT(0), Vector_3(FT(1),FT(0),FT(0)));
       base = Rep(circle.diametral_sphere(), circle.supporting_plane());
     }
   }