diff --git a/dill/session.py b/dill/session.py
index aaf36ec9..6acdd432 100644
--- a/dill/session.py
+++ b/dill/session.py
@@ -308,7 +308,7 @@ def _identify_module(file, main=None):
 
 def load_module(
     filename = str(TEMPDIR/'session.pkl'),
-    module: Union[ModuleType, str] = None,
+    module: Optional[Union[ModuleType, str]] = None,
     **kwds
 ) -> Optional[ModuleType]:
     """Update the selected module (default is :py:mod:`__main__`) with