diff --git a/rohmu/util.py b/rohmu/util.py
index 7738de4c..0ec1790e 100644
--- a/rohmu/util.py
+++ b/rohmu/util.py
@@ -5,12 +5,16 @@
 See LICENSE for details
 """
 from __future__ import annotations
-
+import sys
 from io import BytesIO, UnsupportedOperation
 from itertools import islice
 from rohmu.typing import HasFileno
 from typing import BinaryIO, Generator, Iterable, Optional, Tuple, TypeVar, Union
-from typing_extensions import Buffer
+if sys.version_info < (3, 10):
+    from typing_extensions import Buffer
+else:
+    from typing import ByteString, MutableSequence
+    Buffer = Union[ByteString, MutableSequence[bytes]]
 
 import fcntl
 import logging
@@ -205,10 +209,10 @@ def seek(self, offset: int, whence: int = 0) -> int:
     def truncate(self, size: Optional[int] = None) -> int:
         raise UnsupportedOperation("truncate")
 
-    def write(self, s: Union[bytes, Buffer]) -> int:
+    def write(self, s: Union[bytes, Buffer]) -> int: # type: ignore
         raise UnsupportedOperation("write")
 
-    def writelines(self, __lines: Union[Iterable[bytes], Iterable[Buffer]]) -> None:
+    def writelines(self, __lines: Union[Iterable[bytes], Iterable[Buffer]]) -> None: # type: ignore
         raise UnsupportedOperation("writelines")
 
     def fileno(self) -> int: