diff --git a/pytorch_lightning/trainer/data_loading_mixin.py b/pytorch_lightning/trainer/data_loading_mixin.py
index 7755bc7d5dfef..52541a86fc0cb 100644
--- a/pytorch_lightning/trainer/data_loading_mixin.py
+++ b/pytorch_lightning/trainer/data_loading_mixin.py
@@ -24,7 +24,7 @@ def init_train_dataloader(self, model):
         self.get_train_dataloader = model.train_dataloader
 
         # determine number of training batches
-        if isinstance(self.get_train_dataloader(), IterableDataset):
+        if isinstance(self.get_train_dataloader().dataset, IterableDataset):
             self.nb_training_batches = float('inf')
         else:
             self.nb_training_batches = len(self.get_train_dataloader())
@@ -167,7 +167,7 @@ def get_dataloaders(self, model):
             self.get_val_dataloaders()
 
         # support IterableDataset for train data
-        self.is_iterable_train_dataloader = isinstance(self.get_train_dataloader(), IterableDataset)
+        self.is_iterable_train_dataloader = isinstance(self.get_train_dataloader().dataset, IterableDataset)
         if self.is_iterable_train_dataloader and not isinstance(self.val_check_interval, int):
             m = '''
             When using an iterableDataset for train_dataloader,