diff --git a/Kernel_23/doc_tex/Kernel_23_ref/Aff_transformation_2.tex b/Kernel_23/doc_tex/Kernel_23_ref/Aff_transformation_2.tex
index 765f06f7a01..82144c87a78 100644
--- a/Kernel_23/doc_tex/Kernel_23_ref/Aff_transformation_2.tex
+++ b/Kernel_23/doc_tex/Kernel_23_ref/Aff_transformation_2.tex
@@ -49,7 +49,7 @@ therefore do not appear in the constructors.
              $d$, such that the differences between the sines and cosines
              of the rotation given by d and the approximating rotation
              are at most $num/den$ each.
-             \ccPrecond $num/den>0$. }
+             \ccPrecond $num/den>0$ and $d != 0$. }
 
 \ccConstructor{Aff_transformation_2(const Rotation,
                                        const Kernel::RT &sine_rho, 
diff --git a/Kernel_23/include/CGAL/rational_rotation.h b/Kernel_23/include/CGAL/rational_rotation.h
index 6a2b9b50717..ef3f98ce3e7 100644
--- a/Kernel_23/include/CGAL/rational_rotation.h
+++ b/Kernel_23/include/CGAL/rational_rotation.h
@@ -44,6 +44,7 @@ rational_rotation_approximation( const NT &  dirx,     // dir.x()
   const NT& d   = eps_den;
   const NT  NT0 = NT(0)  ;
   const NT  NT1 = NT(1)  ;
+  CGAL_kernel_precondition( (dirx != NT0) ||  (diry != NT0));
   CGAL_kernel_precondition( n > NT0 );
   CGAL_kernel_precondition( d > NT0 );
   NT & sin = sin_num;