diff --git a/pytorch_lightning/trainer/properties.py b/pytorch_lightning/trainer/properties.py
index 8d509d41d52bf..42b5f7a36641c 100644
--- a/pytorch_lightning/trainer/properties.py
+++ b/pytorch_lightning/trainer/properties.py
@@ -15,7 +15,7 @@
 import os
 from abc import ABC
 from argparse import ArgumentParser, Namespace
-from typing import List, Optional, Union, Type, TypeVar
+from typing import List, Optional, Union, Type, TypeVar, cast
 
 from pytorch_lightning.callbacks import Callback, ProgressBarBase, ModelCheckpoint
 from pytorch_lightning.core.lightning import LightningModule
@@ -154,6 +154,7 @@ def progress_bar_callback(self):
     def progress_bar_dict(self) -> dict:
         """ Read-only for progress bar metrics. """
         ref_model = self.model if not self.data_parallel else self.model.module
+        ref_model = cast(LightningModule, ref_model)
         return dict(**ref_model.get_progress_bar_dict(), **self.logger_connector.progress_bar_metrics)
 
     @property