diff --git a/sdks/python/apache_beam/io/fileio.py b/sdks/python/apache_beam/io/fileio.py
index 378ecf71920d..d9b2a2040675 100644
--- a/sdks/python/apache_beam/io/fileio.py
+++ b/sdks/python/apache_beam/io/fileio.py
@@ -557,6 +557,8 @@ def __init__(
         class signature or an instance of FileSink to this parameter. If none is
         provided, a ``TextSink`` is used.
       shards (int): The number of shards per destination and trigger firing.
+      output_fn (callable, optional): A callable to process the output. This
+        parameter is currently unused and retained for backward compatibility.
       max_writers_per_bundle (int): The number of writers that can be open
         concurrently in a single worker that's processing one bundle.
     """