diff --git a/echopype/mask/api.py b/echopype/mask/api.py
index 33886a420f..5f24ba995a 100644
--- a/echopype/mask/api.py
+++ b/echopype/mask/api.py
@@ -1,7 +1,8 @@
 import datetime
 import operator as op
 import pathlib
-from typing import List, Optional, Union
+import warnings
+from typing import List, Optional, Tuple, Union
 
 import numpy as np
 import xarray as xr