diff --git a/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Shape_base.h b/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Shape_base.h
index 73c1c82bd3d..e0a3e555f7c 100644
--- a/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Shape_base.h
+++ b/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Shape_base.h
@@ -638,7 +638,9 @@ namespace CGAL {
     FT get_x(const Point_3& p) const { return m_traits.compute_x_3_object()(p); }
     FT get_y(const Point_3& p) const { return m_traits.compute_y_3_object()(p); }
     FT get_z(const Point_3& p) const { return m_traits.compute_z_3_object()(p); }
-      
+
+    Vector_3 constr_vec() const
+    { return m_traits.construct_vector_3_object()(NULL_VECTOR); }
     Vector_3 constr_vec(const Point_3& p, const Point_3& q) const
     { return m_traits.construct_vector_3_object()(p, q); }
 
diff --git a/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Sphere.h b/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Sphere.h
index 142b9d2c6a3..dd89eb83ab4 100644
--- a/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Sphere.h
+++ b/Point_set_shape_detection_3/include/CGAL/Shape_detection_3/Sphere.h
@@ -286,7 +286,7 @@ namespace CGAL {
                             FT &cluster_epsilon,
                             FT min[2],
                             FT max[2]) const {
-      Vector_3 axis;
+      Vector_3 axis = this->constr_vec();
       FT rad = radius();
       // Take average normal as axis
       for (std::size_t i = 0;i<indices.size();i++)
@@ -320,6 +320,7 @@ namespace CGAL {
       FT phi = atan2(this->scalar_pdct(vec, d2), this->scalar_pdct(vec, d1));
       FT x = FT(0), y = FT(0);
       concentric_mapping(phi, proj, rad, x, y);
+      CGAL_assertion( x==x && y==y); // check not nan's
 
       min[0] = max[0] = x;
       min[1] = max[1] = y;
@@ -334,6 +335,7 @@ namespace CGAL {
         phi = atan2(this->scalar_pdct(vec, d2), this->scalar_pdct(vec, d1));
 
         concentric_mapping(phi, proj, rad, x, y);
+        CGAL_assertion( x==x && y==y); // check not nan's
 
         min[0] = (std::min<FT>)(min[0], x);
         max[0] = (std::max<FT>)(max[0], x);