diff --git a/009-Extrusion/box.scad b/009-Extrusion/box.scad
index c6e8617..a07f4c9 100644
--- a/009-Extrusion/box.scad
+++ b/009-Extrusion/box.scad
@@ -20,7 +20,7 @@ module box(l, w, h, r, thickness) {
     scale([1,1,-1])
       translate([0,0,-thickness])
         linear_extrude(height=h)
-          rounded_rectangle(l-thickness*2, w-thickness*2, r);
+          rounded_rectangle(l-thickness*2, w-thickness*2, r-thickness);
   }
 }