diff --git a/Number_types/include/CGAL/Lazy_exact_nt.h b/Number_types/include/CGAL/Lazy_exact_nt.h
index f9a5c094ac9..ac784a6eb04 100644
--- a/Number_types/include/CGAL/Lazy_exact_nt.h
+++ b/Number_types/include/CGAL/Lazy_exact_nt.h
@@ -482,7 +482,7 @@ public :
 
   static void set_relative_precision_of_to_double(const double & d)
   {
-      CGAL_assertion(0 < d & d < 1);
+      CGAL_assertion((0 < d) & (d < 1));
       relative_precision_of_to_double = d;
   }