diff --git a/ladybug_geometry/geometry3d/face.py b/ladybug_geometry/geometry3d/face.py
index 1d6863d6..f543dbd8 100644
--- a/ladybug_geometry/geometry3d/face.py
+++ b/ladybug_geometry/geometry3d/face.py
@@ -1170,7 +1170,7 @@ def split_with_line(self, line, tolerance):
             return None
 
         # get BooleanPolygons of the polygon and the line segment
-        move_vec = line_2d.v.rotate(math.pi / 2) * (tolerance / 10)
+        move_vec = line_2d.v.rotate(math.pi / 2).normalize() * (tolerance / 10)
         line_verts = (line_2d.p1, line_2d.p2, line_2d.p2.move(move_vec),
                       line_2d.p1.move(move_vec))
         line_poly = [(pb.BooleanPoint(pt.x, pt.y) for pt in line_verts)]