diff --git a/pytorch_lightning/core/lightning.py b/pytorch_lightning/core/lightning.py
index b648c86843..9cb5171d9f 100644
--- a/pytorch_lightning/core/lightning.py
+++ b/pytorch_lightning/core/lightning.py
@@ -307,7 +307,7 @@ class LightningModule(ABC, GradInformation, ModelIO, ModelHooks):
             val_outs = []
             for val_batch in val_data:
                 out = validation_step(train_batch)
-                val_outs.append(out
+                val_outs.append(out)
                 validation_epoch_end(val_outs)
 
         Args: