diff --git a/torch_em/data/datasets/pannuke.py b/torch_em/data/datasets/pannuke.py
index 2a2a9cb9..df46154f 100644
--- a/torch_em/data/datasets/pannuke.py
+++ b/torch_em/data/datasets/pannuke.py
@@ -4,6 +4,7 @@
 import shutil
 import numpy as np
 from glob import glob
+from typing import List
 
 import torch_em
 from torch_em.data.datasets import util
@@ -144,12 +145,12 @@ def _channels_to_semantics(labels):
 def get_pannuke_dataset(
         path,
         patch_shape,
-        folds=("fold_1", "fold_2", "fold_3"),
+        folds: List[str] = ["fold_1", "fold_2", "fold_3"],
         rois={},
         download=False,
         with_channels=True,
         with_label_channels=False,
-        custom_label_choice="instances",
+        custom_label_choice: str = "instances",
         **kwargs
 ):
     assert custom_label_choice in [
@@ -177,7 +178,7 @@ def get_pannuke_loader(
         path,
         patch_shape,
         batch_size,
-        folds=("fold_1", "fold_2", "fold_3"),
+        folds=["fold_1", "fold_2", "fold_3"],
         download=False,
         rois={},
         custom_label_choice="instances",