diff --git a/stdlib/unittest/util.pyi b/stdlib/unittest/util.pyi
index 845accfeb..c42d1346e 100644
--- a/stdlib/unittest/util.pyi
+++ b/stdlib/unittest/util.pyi
@@ -1,4 +1,4 @@
-from collections.abc import Sequence
+from collections.abc import MutableSequence, Sequence
 from typing import Any, TypeVar
 from typing_extensions import TypeAlias
 
@@ -17,7 +17,7 @@ def _common_shorten_repr(*args: str) -> tuple[str, ...]: ...
 def safe_repr(obj: object, short: bool = False) -> str: ...
 def strclass(cls: type) -> str: ...
 def sorted_list_difference(expected: Sequence[_T], actual: Sequence[_T]) -> tuple[list[_T], list[_T]]: ...
-def unorderable_list_difference(expected: Sequence[_T], actual: Sequence[_T]) -> tuple[list[_T], list[_T]]: ...
+def unorderable_list_difference(expected: MutableSequence[_T], actual: MutableSequence[_T]) -> tuple[list[_T], list[_T]]: ...
 def three_way_cmp(x: Any, y: Any) -> int: ...
 def _count_diff_all_purpose(actual: Sequence[_T], expected: Sequence[_T]) -> list[_Mismatch[_T]]: ...
 def _count_diff_hashable(actual: Sequence[_T], expected: Sequence[_T]) -> list[_Mismatch[_T]]: ...