diff --git a/src/ifcopenshell-python/ifcopenshell/api/geometry/add_door_representation.py b/src/ifcopenshell-python/ifcopenshell/api/geometry/add_door_representation.py
index a4460ce984..6174d9d2d7 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/geometry/add_door_representation.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/geometry/add_door_representation.py
@@ -28,6 +28,7 @@ import ifcopenshell.api.geometry
 import ifcopenshell.util.unit
 from ifcopenshell.api.geometry.add_window_representation import create_ifc_window
 from ifcopenshell.util.shape_builder import ShapeBuilder, V
+from ifcopenshell.util.unit import mm_to_m as mm
 
 DOOR_TYPE = Literal[
     "SINGLE_SWING_LEFT",
@@ -43,11 +44,6 @@ DOOR_TYPE = Literal[
 SUPPORTED_DOOR_TYPES = get_args(DOOR_TYPE)
 
 
-def mm(x: float) -> float:
-    """mm to meters shortcut for readability"""
-    return x / 1000
-
-
 def create_ifc_door_lining(
     builder: ShapeBuilder, size: np.ndarray, thickness: Union[list[float], float], position: Optional[np.ndarray] = None
 ) -> ifcopenshell.entity_instance: