diff --git a/netam/multihit.py b/netam/multihit.py
index 482cb6ec..529f1917 100644
--- a/netam/multihit.py
+++ b/netam/multihit.py
@@ -14,7 +14,7 @@
 from torch.utils.data import Dataset
 from tqdm import tqdm
 import pandas as pd
-from typing import Sequence, List
+from typing import Sequence, List, Tuple
 
 from netam.molevol import (
     reshape_for_codons,
@@ -452,7 +452,7 @@ def hit_class_dataset_from_pcp_df(
 
 def train_test_datasets_of_pcp_df(
     pcp_df: pd.DataFrame, train_frac: float = 0.8, branch_length_multiplier: float = 1.0
-) -> tuple[HitClassDataset, HitClassDataset]:
+) -> Tuple[HitClassDataset, HitClassDataset]:
     """Splits a pcp_df prepared by `prepare_pcp_df` into a training and testing
     HitClassDataset."""
     nt_parents = pcp_df["parent"].reset_index(drop=True)