diff --git a/Poisson_surface_reconstruction_3/include/CGAL/Poisson_reconstruction_function.h b/Poisson_surface_reconstruction_3/include/CGAL/Poisson_reconstruction_function.h
index ea3b31413ac3..23bb0f269339 100644
--- a/Poisson_surface_reconstruction_3/include/CGAL/Poisson_reconstruction_function.h
+++ b/Poisson_surface_reconstruction_3/include/CGAL/Poisson_reconstruction_function.h
@@ -1128,7 +1128,7 @@ class Poisson_reconstruction_function
     }
     while(circ != done);
 
-    CGAL_assertion(! voronoi_points.size() < 3);
+    CGAL_assertion(! (voronoi_points.size() < 3));
 
     // sum up areas
     FT area = 0.0;