diff --git a/pyproject.toml b/pyproject.toml
index ec488de..ca54350 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -89,7 +89,6 @@ ignore = [
     "PERF401",
     "ARG003",
     "ANN001",
-    "ANN201",
 ]
 
 [tool.mypy]
diff --git a/raillabel/save/save.py b/raillabel/save/save.py
index 8778441..14d2901 100644
--- a/raillabel/save/save.py
+++ b/raillabel/save/save.py
@@ -7,7 +7,7 @@
 from ..format import Scene
 
 
-def save(scene: Scene, path: str, prettify_json: bool = False):
+def save(scene: Scene, path: str, prettify_json: bool = False) -> None:
     """Save a raillabel.Scene in a JSON file.
 
     Parameters