diff --git a/python/deltalake/fs.py b/python/deltalake/fs.py
index 46b8ab9252..d13a1801ba 100644
--- a/python/deltalake/fs.py
+++ b/python/deltalake/fs.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Mapping, Optional
 
 import pyarrow as pa
 from pyarrow.fs import FileInfo, FileSelector, FileSystemHandler
@@ -152,5 +152,5 @@ def get_file_info_selector(self, selector: FileSelector) -> List[FileInfo]:  # t
             selector.base_dir, selector.allow_not_found, selector.recursive
         )
 
-    def open_append_stream(path: str, metadata: dict):
+    def open_append_stream(self, path: str, metadata: Mapping):
         raise NotImplementedError