diff --git a/Alpha_shapes_2/include/CGAL/Alpha_shape_2.h b/Alpha_shapes_2/include/CGAL/Alpha_shape_2.h
index 3c4cb4b7d30..812f609d3ac 100644
--- a/Alpha_shapes_2/include/CGAL/Alpha_shape_2.h
+++ b/Alpha_shapes_2/include/CGAL/Alpha_shape_2.h
@@ -1442,7 +1442,7 @@ Alpha_shape_2<Dt,EACT>::find_alpha_solid() const
   // takes O(#alpha_shape) time
   Type_of_alpha alpha_solid = 0;
 
-  if (number_of_vertices()<3) return alpha_solid;
+  if (dimension()!=2) return alpha_solid;
 
   Finite_vertices_iterator vertex_it;
   // only finite vertices