diff --git a/sdks/python/apache_beam/io/iobase.py b/sdks/python/apache_beam/io/iobase.py
index 67d6cd358a07..229d124a5726 100644
--- a/sdks/python/apache_beam/io/iobase.py
+++ b/sdks/python/apache_beam/io/iobase.py
@@ -1212,7 +1212,7 @@ def _expand_bounded(self, pcoll, min_shards):
             AsSingleton(init_result_coll),
             AsIter(write_result_coll),
             min_shards,
-            AsSingleton(pre_finalize_coll)).with_output_types(str))
+            AsSingleton(pre_finalize_coll)))
 
   def _apply_windowing(self, pcoll):
     """