diff --git a/pytorch_lightning/models/trainer.py b/pytorch_lightning/models/trainer.py
index eb80300f..82a24e9e 100644
--- a/pytorch_lightning/models/trainer.py
+++ b/pytorch_lightning/models/trainer.py
@@ -380,7 +380,7 @@ class Trainer(TrainerIO):
         :return:
         """
         try:
-            os.environ['MASTER_PORT']
+            port = os.environ['MASTER_PORT']
         except Exception as e:
             port = 12910
             os.environ['MASTER_PORT'] = f'{port}'