diff --git a/torch/utils/data/datapipes/iter/filelister.py b/torch/utils/data/datapipes/iter/filelister.py
index 9de99cf9b4a..2b3d16bed2a 100644
--- a/torch/utils/data/datapipes/iter/filelister.py
+++ b/torch/utils/data/datapipes/iter/filelister.py
@@ -1,4 +1,3 @@
-# mypy: allow-untyped-defs
 from collections.abc import Iterator, Sequence
 from typing import Union
 
@@ -63,7 +62,7 @@ class FileListerIterDataPipe(IterDataPipe[str]):
                 path, self.masks, self.recursive, self.abspath, self.non_deterministic
             )
 
-    def __len__(self):
+    def __len__(self) -> int:
         if self.length == -1:
             raise TypeError(f"{type(self).__name__} instance doesn't have valid length")
         return self.length