diff --git a/Kernel_23/include/CGAL/Kernel/function_objects.h b/Kernel_23/include/CGAL/Kernel/function_objects.h
index ead2582c6bc2..9b6af428e25b 100644
--- a/Kernel_23/include/CGAL/Kernel/function_objects.h
+++ b/Kernel_23/include/CGAL/Kernel/function_objects.h
@@ -244,6 +244,7 @@ namespace CommonKernelFunctors {
 
       const Vector_3 abac1 = xproduct(ab1, ac1);
       const Vector_3 abad1 = xproduct(ab1, ad1);
+      if (abac1==NULL_VECTOR || abad1==NULL_VECTOR) return SMALLER;
       const FT sc_prod_1 = abac1 * abad1;
 
       CGAL_kernel_assertion_msg( abac1 != NULL_VECTOR,