diff --git a/grain/_src/python/dataset/transformations/batch.py b/grain/_src/python/dataset/transformations/batch.py
index 2ba2c690..1fdc4281 100644
--- a/grain/_src/python/dataset/transformations/batch.py
+++ b/grain/_src/python/dataset/transformations/batch.py
@@ -86,9 +86,8 @@ def __call__(self, values: Sequence[T]) -> T:
     def _batch_fn(*xs: Sequence[T]) -> T:
       # If the thread pool is not available or the elements are not NumPy
       # arrays, fall back to the standard serial `np.stack` operation.
-      if (self._parallel_batch_executor is None) or not isinstance(
-          xs[0], np.ndarray
-      ):
+      all_ndarray = all(isinstance(x, np.ndarray) for x in xs)
+      if (self._parallel_batch_executor is None) or not all_ndarray:
         return np.stack(xs)
       xs = cast(Sequence[np.ndarray], xs)
       # Fall back to the standard serial `np.stack` operation if the size of
diff --git a/grain/_src/python/dataset/transformations/batch_test.py b/grain/_src/python/dataset/transformations/batch_test.py
index 02f9d66b..9a48f5bc 100644
--- a/grain/_src/python/dataset/transformations/batch_test.py
+++ b/grain/_src/python/dataset/transformations/batch_test.py
@@ -69,6 +69,13 @@ def test_batch_single_value_parallel_batch_enabled_success(self):
     batched_values = make_batch_parallel(values)
     self.assertEqual(batched_values.shape, (1, 3))
 
+  def test_batch_non_numpy_values(self):
+    values = [np.asarray([1, 2, 3]), [4, 5, 6]]
+    make_batch_parallel = batch._MakeBatchParallel()
+    batched_values = make_batch_parallel(values)
+    self.assertIsInstance(batched_values, np.ndarray)
+    self.assertEqual(batched_values.shape, (2, 3))
+
   def test_batch_two_values_success(self):
     values = [np.asarray([1, 2, 3]), np.asarray([4, 5, 6])]
     batched_values = batch.make_batch(values)