diff --git a/capytaine/matrices/block.py b/capytaine/matrices/block.py
index 4fd14cf6..7fb7f91f 100644
--- a/capytaine/matrices/block.py
+++ b/capytaine/matrices/block.py
@@ -185,7 +185,9 @@ def full_matrix(self, dtype=None) -> np.ndarray:
         self._put_in_full_matrix(full_matrix)
         return full_matrix
 
-    def __array__(self, dtype=None):
+    def __array__(self, dtype=None, copy=True):
+        if not copy:
+            raise ValueError("Making an ndarray out of a BlockMatrix requires copy")
         return self.full_matrix(dtype=dtype)
 
     def no_toeplitz(self):
@@ -587,4 +589,4 @@ def access_block_by_path(self, path):
         this_block = self
         for index in path:
             this_block = this_block.all_blocks[index, index]
-        return this_block
\ No newline at end of file
+        return this_block
diff --git a/capytaine/matrices/low_rank.py b/capytaine/matrices/low_rank.py
index 82e3c2ae..c2eb302e 100644
--- a/capytaine/matrices/low_rank.py
+++ b/capytaine/matrices/low_rank.py
@@ -318,7 +318,9 @@ def full_matrix(self, dtype=None):
         else:
             return self.left_matrix @ self.right_matrix
 
-    def __array__(self, dtype=None):
+    def __array__(self, dtype=None, copy=True):
+        if not copy:
+            raise ValueError("Making an ndarray out of a BlockMatrix requires copy")
         return self.full_matrix(dtype=dtype)
 
     @property
diff --git a/capytaine/meshes/meshes.py b/capytaine/meshes/meshes.py
index c5fd48dc..7ec88e6f 100644
--- a/capytaine/meshes/meshes.py
+++ b/capytaine/meshes/meshes.py
@@ -809,7 +809,8 @@ def generate_lid(self, z=0.0, faces_max_radius=None):
         # edges_of_hull_faces.shape = (nb_full_faces, 4, 2)
         lid_points_in_local_coords = candidate_lid_points[:, np.newaxis, np.newaxis, :] - hull_faces[:, :, :]
         # lid_points_in_local_coords.shape = (nb_candidate_lid_points, nb_full_faces, 4, 2)
-        side_of_hull_edges = np.cross(lid_points_in_local_coords, edges_of_hull_faces)
+        side_of_hull_edges = (lid_points_in_local_coords[..., 0] * edges_of_hull_faces[..., 1]
+                             - lid_points_in_local_coords[..., 1] * edges_of_hull_faces[..., 0])
         # side_of_hull_edges.shape = (nb_candidate_lid_points, nb_full_faces, 4)
         point_is_above_panel = np.all(side_of_hull_edges <= 0, axis=-1) | np.all(side_of_hull_edges >= 0, axis=-1)
         # point_is_above_panel.shape = (nb_candidate_lid_points, nb_full_faces)