diff --git a/python/metatensor-torch/metatensor/torch/atomistic/ase_calculator.py b/python/metatensor-torch/metatensor/torch/atomistic/ase_calculator.py
index 8d86e112c..e4f2abfde 100644
--- a/python/metatensor-torch/metatensor/torch/atomistic/ase_calculator.py
+++ b/python/metatensor-torch/metatensor/torch/atomistic/ase_calculator.py
@@ -238,7 +238,7 @@ def calculate(
         atoms: ase.Atoms,
         properties: List[str],
         system_changes: List[str],
-    ) -> Dict[str, np.ndarray]:
+    ) -> None:
         """
         Compute some ``properties`` with this calculator, and return them in the format
         expected by ASE.