diff --git a/orderly_set/sets.py b/orderly_set/sets.py
index e9435b1..13b3f04 100644
--- a/orderly_set/sets.py
+++ b/orderly_set/sets.py
@@ -377,7 +377,7 @@ def index(self, value: Hashable) -> int:
         except ValueError:
             raise KeyError(value)
 
-    def indexes(self, keys: list[Hashable]) -> list[int]:
+    def indexes(self, keys: List[Hashable]) -> List[int]:
         return [self.index(subkey) for subkey in keys]
 
     # Provide some compatibility with pd.Index
@@ -962,7 +962,7 @@ def update(self, sequence: SetLike[T]) -> int:
     def index(self, value: Hashable) -> int:
         return self._map[value]
 
-    def indexes(self, keys: list[Hashable]) -> list[int]:
+    def indexes(self, keys: List[Hashable]) -> List[int]:
         return [self._map[key] for key in keys]
 
     def pop(self, index: int = -1) -> T:
@@ -1237,7 +1237,7 @@ def index(self, key: Hashable) -> Any:
         except ValueError:
             raise KeyError(key)
 
-    def indexes(self, keys: list[Hashable]) -> list[int]:
+    def indexes(self, keys: List[Hashable]) -> List[int]:
         return [self.index(subkey) for subkey in keys]
 
     # Provide some compatibility with pd.Index