diff --git a/python/chemiscope/structures/_shapes.py b/python/chemiscope/structures/_shapes.py
index 1113bb847..b52346ac6 100644
--- a/python/chemiscope/structures/_shapes.py
+++ b/python/chemiscope/structures/_shapes.py
@@ -101,7 +101,7 @@ def ellipsoid_from_tensor(tensor, scale=1.0, force_positive=False):
     a positive definite tensor (e.g. a polarizability), in the form
     required by the chemiscope input.
 
-    :param tensor: a positive-definite tensor (3x3 or 6 array)
+    :param tensor: a positive-definite tensor (3x3 or a 6-array [xx,yy,zz,xy,xz,yz])
     :param scale: conversion from the units of the tensor to the units of the atomic positions (usually Å)
     :param force_positive: takes the absolute value of eigenvalues, to handle non-positive tensors
     """