diff --git a/surface_apps/iso_surfaces/utils.py b/surface_apps/iso_surfaces/utils.py
index 28a771f..35ed533 100644
--- a/surface_apps/iso_surfaces/utils.py
+++ b/surface_apps/iso_surfaces/utils.py
@@ -105,8 +105,6 @@ def interp_to_grid(  # pylint: disable=too-many-locals
     grid = []
     is_finite = np.isfinite(data.values)
     if isinstance(entity, CellObject) and data.association == DataAssociationEnum.CELL:
-        if entity.vertices is None:
-            raise ValueError("Entity must contain vertices.")
         locations = np.mean(entity.vertices[entity.cells], axis=1)[is_finite, :]
     else:
         locations = entity.locations[is_finite, :]
@@ -154,21 +152,18 @@ def extract_iso_surfaces(
             verts, faces, _normals, _values = marching_cubes(values, level=level)
             verts, faces = remove_nan(verts, faces)
 
-            vertices = []
+            vertices = np.empty((len(verts), 3), dtype=float)
             for i in np.arange(3):
                 interp = interp1d(
                     np.arange(grid[i].shape[0]), grid[i], fill_value="extrapolate"
                 )
-                vertices += [interp(verts[:, i])]
+                vertices[:, i] = interp(verts[:, i])
 
             if isinstance(entity, BlockModel):
-                vertices = rotate_xyz(np.vstack(vertices).T, [0, 0, 0], entity.rotation)
-                vertices[:, 0] += entity.origin["x"]  # type: ignore
-                vertices[:, 1] += entity.origin["y"]  # type: ignore
-                vertices[:, 2] += entity.origin["z"]  # type: ignore
-
-            else:
-                vertices = np.vstack(vertices).T  # type: ignore
+                vertices = rotate_xyz(vertices, [0, 0, 0], entity.rotation)
+                vertices[:, 0] += entity.origin[0]
+                vertices[:, 1] += entity.origin[1]
+                vertices[:, 2] += entity.origin[2]
 
         except RuntimeError as _:
             logging.exception("Caught a RuntimeError in marching cubes algorithm.")
diff --git a/tests/run_tests/iso_surfaces_test.py b/tests/run_tests/iso_surfaces_test.py
index ae4e42e..e16337f 100644
--- a/tests/run_tests/iso_surfaces_test.py
+++ b/tests/run_tests/iso_surfaces_test.py
@@ -83,15 +83,6 @@ def test_centroids(tmp_path: Path):
         ((sphere_center + origin) - surf_center) / (sphere_center + origin)
     )
 
-    assert np.all(center_error < 0.02)
-
-    # Radius of sphere
-    surf_distance = np.linalg.norm(np.subtract(func_surface[0][0], surf_center), axis=1)
-    surf_radius = np.mean(surf_distance, axis=0)
-    radius_error = np.abs((surf_radius - sphere_radius) / sphere_radius)
-
-    assert radius_error < 0.02
-
     # For user validation only
     Surface.create(
         ws, name="surface", vertices=func_surface[0][0], cells=func_surface[0][1]
@@ -105,6 +96,15 @@ def test_centroids(tmp_path: Path):
     )
     ws.close()
 
+    assert np.all(center_error < 0.02)
+
+    # Radius of sphere
+    surf_distance = np.linalg.norm(np.subtract(func_surface[0][0], surf_center), axis=1)
+    surf_radius = np.mean(surf_distance, axis=0)
+    radius_error = np.abs((surf_radius - sphere_radius) / sphere_radius)
+
+    assert radius_error < 0.02
+
 
 def test_vertices(tmp_path: Path):
     """