diff --git a/tests/torchtune/datasets/test_concat_dataset.py b/tests/torchtune/datasets/test_concat_dataset.py
index 32ecc3bc5a..352d20e372 100644
--- a/tests/torchtune/datasets/test_concat_dataset.py
+++ b/tests/torchtune/datasets/test_concat_dataset.py
@@ -6,7 +6,25 @@
 
 import pytest
 from datasets import Dataset
+from torch.utils.data import Dataset as TorchDataset
 from torchtune.datasets._concat import ConcatDataset
+from torchtune.datasets._packed import PackedDataset
+
+
+class DummyDataset(TorchDataset):
+    def __init__(self, sample_size):
+        self.sample_size = sample_size
+
+    def __getitem__(self, index):
+        if index >= 1000:
+            raise IndexError()
+        return {
+            "tokens": [index] * self.sample_size,
+            "labels": [index] * self.sample_size,
+        }
+
+    def __len__(self):
+        return 1000
 
 
 class TestConcatDataset:
@@ -20,6 +38,16 @@ def datasets(self):
         ds6 = Dataset.from_list([{"data": f"ds6_{i}"} for i in range(42)])
         return [ds1, ds2, ds3, ds4, ds5, ds6]
 
+    @pytest.fixture
+    def torch_datasets(self):
+        ds1 = DummyDataset(4)
+        ds2 = DummyDataset(8)
+        ds3 = DummyDataset(15)
+        ds4 = DummyDataset(16)
+        ds5 = DummyDataset(23)
+        ds6 = DummyDataset(42)
+        return [ds1, ds2, ds3, ds4, ds5, ds6]
+
     def test_length(self, datasets):
         """Test the correct computation of total length"""
         multi_dataset = ConcatDataset(datasets)
@@ -51,3 +79,14 @@ def test_invalid_index_type(self, datasets):
 
         with pytest.raises(TypeError):
             multi_dataset["invalid_type"]  # Non-integer index
+
+    def test_packed_dataset(self, torch_datasets):
+        torch_datasets[0] = PackedDataset(
+            torch_datasets[0],
+            max_seq_len=25,
+            max_packs=5,
+            split_across_pack=True,
+        )
+
+        with pytest.raises(ValueError):
+            concated_dataset = ConcatDataset(torch_datasets)
diff --git a/torchtune/datasets/_concat.py b/torchtune/datasets/_concat.py
index 2a76602697..304a605641 100644
--- a/torchtune/datasets/_concat.py
+++ b/torchtune/datasets/_concat.py
@@ -10,6 +10,8 @@
 
 from torchtune import utils
 
+from torchtune.datasets._packed import PackedDataset
+
 log = utils.get_logger("DEBUG")
 
 
@@ -35,6 +37,9 @@ class ConcatDataset(Dataset):
         datasets (List[Dataset]): A list of datasets to concatenate. Each dataset must be an instance of a class
             derived from :class:`~torch.utils.data.Dataset`.
 
+    Raises:
+        ValueError: if instanse of `PackedDataset` is in `datasets`
+
     Examples:
         >>> dataset1 = MyCustomDataset(params1)
         >>> dataset2 = MyCustomDataset(params2)
@@ -64,6 +69,13 @@ class ConcatDataset(Dataset):
 
     def __init__(self, datasets: List[Dataset]):
         self._datasets: List[Dataset] = datasets
+
+        for dataset in self._datasets:
+            if isinstance(dataset, PackedDataset):
+                raise ValueError(
+                    "ConcatDataset can't process instances of PackedDataset."
+                )
+
         self._len: int = sum(len(dataset) for dataset in datasets)
         self._indexes: List[Tuple[int, int, int]] = []