diff --git a/libs/core/langchain_core/utils/aiter.py b/libs/core/langchain_core/utils/aiter.py
index 8d74a50fb7..245cad098b 100644
--- a/libs/core/langchain_core/utils/aiter.py
+++ b/libs/core/langchain_core/utils/aiter.py
@@ -323,25 +323,35 @@ class aclosing(AbstractAsyncContextManager[Any]):  # noqa: N801
 
 
 async def abatch_iterate(
-    size: int, iterable: AsyncIterable[T]
+    size: int | None, iterable: AsyncIterable[T]
 ) -> AsyncIterator[list[T]]:
     """Utility batching function for async iterables.
 
     Args:
         size: The size of the batch.
+
+            If `None`, returns a single batch.
         iterable: The async iterable to batch.
 
     Yields:
         The batches.
+
+    Raises:
+        ValueError: If `size` is not `None` and is not a positive integer.
     """
+    if size is None:
+        single_batch = [el async for el in iterable]
+        if single_batch:
+            yield single_batch
+        return
+    if size <= 0:
+        msg = f"Batch size must be a positive integer, got {size}."
+        raise ValueError(msg)
     batch: list[T] = []
     async for element in iterable:
-        if len(batch) < size:
-            batch.append(element)
-
+        batch.append(element)
         if len(batch) >= size:
             yield batch
             batch = []
-
     if batch:
         yield batch
diff --git a/libs/core/langchain_core/utils/iter.py b/libs/core/langchain_core/utils/iter.py
index b24c5f213a..b89bddb9fc 100644
--- a/libs/core/langchain_core/utils/iter.py
+++ b/libs/core/langchain_core/utils/iter.py
@@ -214,7 +214,13 @@ def batch_iterate(size: int | None, iterable: Iterable[T]) -> Iterator[list[T]]:
 
     Yields:
         The batches of the iterable.
+
+    Raises:
+        ValueError: If `size` is not `None` and is not a positive integer.
     """
+    if size is not None and size <= 0:
+        msg = f"Batch size must be a positive integer, got {size}."
+        raise ValueError(msg)
     it = iter(iterable)
     while True:
         chunk = list(islice(it, size))
diff --git a/libs/core/tests/unit_tests/utils/test_aiter.py b/libs/core/tests/unit_tests/utils/test_aiter.py
index 078fbdf8ac..a2f903a474 100644
--- a/libs/core/tests/unit_tests/utils/test_aiter.py
+++ b/libs/core/tests/unit_tests/utils/test_aiter.py
@@ -12,10 +12,14 @@ from langchain_core.utils.aiter import abatch_iterate
         (3, [10, 20, 30, 40, 50], [[10, 20, 30], [40, 50]]),
         (1, [100, 200, 300], [[100], [200], [300]]),
         (4, [], []),
+        (None, [1, 2, 3], [[1, 2, 3]]),
+        (None, [], []),
     ],
 )
 async def test_abatch_iterate(
-    input_size: int, input_iterable: list[str], expected_output: list[list[str]]
+    input_size: int | None,
+    input_iterable: list[str],
+    expected_output: list[list[str]],
 ) -> None:
     """Test batching function."""
 
@@ -29,3 +33,15 @@ async def test_abatch_iterate(
 
     output = [el async for el in iterator_]
     assert output == expected_output
+
+
+@pytest.mark.parametrize("input_size", [0, -1])
+async def test_abatch_iterate_invalid_size(input_size: int) -> None:
+    """Non-positive sizes should raise instead of silently discarding data."""
+
+    async def _to_async_iterable(iterable: list[int]) -> AsyncIterator[int]:
+        for item in iterable:
+            yield item
+
+    with pytest.raises(ValueError, match="positive integer"):
+        _ = [el async for el in abatch_iterate(input_size, _to_async_iterable([1, 2]))]
diff --git a/libs/core/tests/unit_tests/utils/test_iter.py b/libs/core/tests/unit_tests/utils/test_iter.py
index 84e7882d48..a3494a3ae0 100644
--- a/libs/core/tests/unit_tests/utils/test_iter.py
+++ b/libs/core/tests/unit_tests/utils/test_iter.py
@@ -10,10 +10,21 @@ from langchain_core.utils.iter import batch_iterate
         (3, [10, 20, 30, 40, 50], [[10, 20, 30], [40, 50]]),
         (1, [100, 200, 300], [[100], [200], [300]]),
         (4, [], []),
+        (None, [1, 2, 3], [[1, 2, 3]]),
+        (None, [], []),
     ],
 )
 def test_batch_iterate(
-    input_size: int, input_iterable: list[str], expected_output: list[list[str]]
+    input_size: int | None,
+    input_iterable: list[str],
+    expected_output: list[list[str]],
 ) -> None:
     """Test batching function."""
     assert list(batch_iterate(input_size, input_iterable)) == expected_output
+
+
+@pytest.mark.parametrize("input_size", [0, -1])
+def test_batch_iterate_invalid_size(input_size: int) -> None:
+    """Non-positive sizes should raise instead of silently discarding data."""
+    with pytest.raises(ValueError, match="positive integer"):
+        list(batch_iterate(input_size, [1, 2, 3]))