diff --git a/conflict_set.py b/conflict_set.py
index 4731647..0cc250c 100644
--- a/conflict_set.py
+++ b/conflict_set.py
@@ -2,6 +2,8 @@ import ctypes
 import enum
 import os
 
+from typing import Optional
+
 _lib = None
 for f in (
     os.path.dirname(__file__) + "/build/radix_tree/libconflict-set.so.0",
@@ -63,7 +65,7 @@ class Result(enum.Enum):
     TOO_OLD = 2
 
 
-def write(begin: bytes, end: bytes | None = None) -> WriteRange:
+def write(begin: bytes, end: Optional[bytes] = None) -> WriteRange:
     b = (ctypes.c_ubyte * len(begin))()
     b.value = begin
     if end is None:
@@ -75,7 +77,7 @@ def write(begin: bytes, end: bytes | None = None) -> WriteRange:
     return WriteRange(_Key(b, len(b)), _Key(e, len(e)))
 
 
-def read(version: int, begin: bytes, end: bytes = None) -> ReadRange:
+def read(version: int, begin: bytes, end: Optional[bytes] = None) -> ReadRange:
     b = (ctypes.c_ubyte * len(begin))()
     b.value = begin
     if end is None: