diff --git a/src/packaging/version.py b/src/packaging/version.py
index e5c738cf..b30e8cbf 100644
--- a/src/packaging/version.py
+++ b/src/packaging/version.py
@@ -10,7 +10,7 @@
 import collections
 import itertools
 import re
-from typing import Callable, Optional, SupportsInt, Tuple, Union
+from typing import Any, Callable, Optional, SupportsInt, Tuple, Union
 
 from ._structures import Infinity, InfinityType, NegativeInfinity, NegativeInfinityType
 
@@ -63,7 +63,7 @@ class InvalidVersion(ValueError):
 
 
 class _BaseVersion:
-    _key: CmpKey
+    _key: Tuple[Any, ...]
 
     def __hash__(self) -> int:
         return hash(self._key)
@@ -179,6 +179,7 @@ class Version(_BaseVersion):
     """
 
     _regex = re.compile(r"^\s*" + VERSION_PATTERN + r"\s*$", re.VERBOSE | re.IGNORECASE)
+    _key: CmpKey
 
     def __init__(self, version: str) -> None:
         """Initialize a Version object.