diff --git a/src/dask_awkward/lib/core.py b/src/dask_awkward/lib/core.py
index 2585661e1..f41cda083 100644
--- a/src/dask_awkward/lib/core.py
+++ b/src/dask_awkward/lib/core.py
@@ -975,7 +975,7 @@ def repartition(
 
     def __len__(self) -> int:
         if not self.known_divisions:
-            raise NotImplementedError(
+            raise TypeError(
                 "Cannot determine length of collection with unknown partition sizes without executing the graph.\n"
                 "Use `dask_awkward.num(..., axis=0)` if you want a lazy Scalar of the length.\n"
                 "If you want to eagerly compute the partition sizes to have the ability to call `len` on the collection"
diff --git a/tests/test_core.py b/tests/test_core.py
index 5d9c9a4e6..0c5f8adfe 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -104,7 +104,7 @@ def test_len(ndjson_points_file: str) -> None:
     daa = dak.from_json([ndjson_points_file] * 2)
     assert not daa.known_divisions
     with pytest.raises(
-        NotImplementedError,
+        TypeError,
         match=(
             "Cannot determine length of collection with unknown partition sizes without executing the graph.\\n"
             "Use `dask_awkward.num\\(\\.\\.\\., axis=0\\)` if you want a lazy Scalar of the length.\\n"
diff --git a/tests/test_io_json.py b/tests/test_io_json.py
index 4837602ee..71f835bb1 100644
--- a/tests/test_io_json.py
+++ b/tests/test_io_json.py
@@ -60,7 +60,7 @@ def test_json_sanity(json_data_dir: Path, concrete_data: ak.Array) -> None:
     ds = dak.from_json(source)
     assert not ds.known_divisions
     with pytest.raises(
-        NotImplementedError,
+        TypeError,
         match=(
             "Cannot determine length of collection with unknown partition sizes without executing the graph.\\n"
             "Use `dask_awkward.num\\(\\.\\.\\., axis=0\\)` if you want a lazy Scalar of the length.\\n"