diff --git a/metalearners/_typing.py b/metalearners/_typing.py
index 10a6f4d..5643f19 100644
--- a/metalearners/_typing.py
+++ b/metalearners/_typing.py
@@ -6,6 +6,7 @@
 
 import numpy as np
 import pandas as pd
+import polars as pl
 import scipy.sparse as sps
 
 PredictMethod = Literal["predict", "predict_proba"]
@@ -21,8 +22,8 @@
 Features = Collection[str] | Collection[int] | None
 
 # ruff is not happy about the usage of Union.
-Vector = Union[pd.Series, np.ndarray]  # noqa
-Matrix = Union[pd.DataFrame, np.ndarray, sps.csr_matrix]  # noqa
+Vector = Union[pd.Series, np.ndarray, pl.Series]  # noqa
+Matrix = Union[pd.DataFrame, np.ndarray, sps.csr_matrix, pl.DataFrame]  # noqa
 
 
 class _ScikitModel(Protocol):