diff --git a/tinydb/table.py b/tinydb/table.py
index 17a0fb60..7083b55c 100644
--- a/tinydb/table.py
+++ b/tinydb/table.py
@@ -3,7 +3,7 @@
 data in TinyDB.
 """
 
-from collections.abc import Callable, Iterable, Iterator, Mapping
+from collections.abc import Callable, Iterable, Iterator, Mapping, MutableMapping
 from typing import (
     NoReturn,
     Optional,
@@ -403,7 +403,7 @@ def contains(
 
     def update(
         self,
-        fields: Union[Mapping, Callable[[Mapping], None]],
+        fields: Union[Mapping, Callable[[MutableMapping], None]],
         cond: Optional[QueryLike] = None,
         doc_ids: Optional[Iterable[int]] = None,
     ) -> list[int]: