diff --git a/bindings/python/pinocchio/visualize/meshcat_visualizer.py b/bindings/python/pinocchio/visualize/meshcat_visualizer.py
index 1b8a3282b..395766f09 100644
--- a/bindings/python/pinocchio/visualize/meshcat_visualizer.py
+++ b/bindings/python/pinocchio/visualize/meshcat_visualizer.py
@@ -69,8 +69,12 @@ def hasMeshFileInfo(geometry_object):
     return False
 
 
-def applyScalingOnHomegeneousTransform(homogeneous_transform, scale):
-    scale = np.asarray(scale).flatten()
+def applyScalingOnHomegeneousTransform(
+    homogeneous_transform: np.ndarray, scale: np.ndarray
+) -> np.ndarray:
+    assert homogeneous_transform.shape == (4, 4)
+    assert scale.shape == (3,)
+    scale = np.array(scale).flatten()
     S = np.diag(np.concatenate((scale, [1.0])))
     return homogeneous_transform @ S