diff --git a/pypots/utils/visualization.py b/pypots/utils/visualization.py
index 282b9e63..69d0ffde 100644
--- a/pypots/utils/visualization.py
+++ b/pypots/utils/visualization.py
@@ -5,6 +5,8 @@
 # Created by Bhargav Vemuri <vemuri.bhargav@gmail.com>
 # License: GPL-v3
 
+from typing import Dict
+
 import numpy as np
 import pandas as pd
 import matplotlib.pyplot as plt
@@ -14,8 +16,7 @@
 
 def get_cluster_members(
     test_data: np.ndarray, class_predictions: np.ndarray
-) #-> dict[int, np.ndarray]
-:
+) -> Dict[int, np.ndarray]:
     """
     Subset time series array using predicted cluster membership.
 
@@ -40,7 +41,7 @@ def get_cluster_members(
 
 def clusters_for_plotting(
     cluster_members: dict[int, np.ndarray],
-) -> dict[int, dict]:
+) -> Dict[int, dict]:
     """
     Organize clustered arrays into format ready for plotting.
 
@@ -132,7 +133,7 @@ def plot_clusters(dict_to_plot: dict[int, dict]) -> None:
             plt.show()
 
 
-def get_cluster_means(dict_to_plot: dict[int, dict]) -> dict[int, dict]:
+def get_cluster_means(dict_to_plot: dict[int, dict]) -> Dict[int, dict]:
     """
     Get time series variables' mean values and 95% confidence intervals at each time point per cluster.