diff --git a/python/chemiscope/structures/_shapes.py b/python/chemiscope/structures/_shapes.py
index 5c84c9d5b..ae06c1957 100644
--- a/python/chemiscope/structures/_shapes.py
+++ b/python/chemiscope/structures/_shapes.py
@@ -146,8 +146,12 @@ def ellipsoid_from_tensor(tensor, scale=1.0, force_positive=False):
     rotation = eigenvectors.T
 
     # converts to quaternion
-    from scipy.spatial.transform import Rotation
-
+    try:
+        from scipy.spatial.transform import Rotation
+    except ImportError as e:
+        raise RuntimeError(
+            "scipy is required to construct arrow shapes"
+        ) from e
     quaternion = Rotation.from_matrix(rotation).as_quat()
 
     return dict(