diff --git a/Circular_kernel_3/include/CGAL/Circular_kernel_3/get_equation_object_on_curved_kernel_3.h b/Circular_kernel_3/include/CGAL/Circular_kernel_3/get_equation_object_on_curved_kernel_3.h
index 7945c924330..ebbe0c92967 100644
--- a/Circular_kernel_3/include/CGAL/Circular_kernel_3/get_equation_object_on_curved_kernel_3.h
+++ b/Circular_kernel_3/include/CGAL/Circular_kernel_3/get_equation_object_on_curved_kernel_3.h
@@ -39,7 +39,6 @@ namespace CGAL {
   {
     public:
 
-    typedef void result_type; // should we keep this?
 
     typedef typename SK::Polynomial_for_spheres_2_3 result_type_for_sphere;
     typedef typename SK::Polynomial_1_3 result_type_for_plane;
@@ -47,6 +46,32 @@ namespace CGAL {
     typedef typename SK::Polynomials_for_circle_3 result_type_for_circle;
     //using LinearFunctors::Get_equation<SK>::operator();
 
+    template <typename>
+    struct result;
+
+    template <typename F>
+    struct result<F(typename SK::Sphere_3)>
+    {
+      typedef result_type_for_sphere type;
+    };
+
+    template <typename F>
+    struct result<F(typename SK::Plane_3)>
+    {
+      typedef result_type_for_plane type;
+    };
+
+    template <typename F>
+    struct result<F(typename SK::Line_3)>
+    {
+      typedef result_type_for_line type;
+    };
+
+    template <typename F>
+    struct result<F(typename SK::Circle_3)>
+    {
+      typedef result_type_for_circle type;
+    };
 
     result_type_for_sphere
     operator() ( const typename SK::Sphere_3 & s )