diff --git a/src/fpm_risk_model/risk_model.py b/src/fpm_risk_model/risk_model.py
index 5b2c839..5b9fb3d 100644
--- a/src/fpm_risk_model/risk_model.py
+++ b/src/fpm_risk_model/risk_model.py
@@ -112,9 +112,9 @@ def _to_numpy(values: Union[ndarray, DataFrame]) -> ndarray:
         if values is None:
             return values
         elif isinstance(values, (DataFrame, Series)):
-            return np.array(values.values)
+            return values.values
         elif isinstance(values, ndarray):
-            return np.array(values)
+            return values
         else:
             raise TypeError(
                 "Expect either pandas DataFrame or numpy array, "