diff --git a/lib/rbx_loader/src/union.rs b/lib/rbx_loader/src/union.rs
index 5a9a492..a291920 100644
--- a/lib/rbx_loader/src/union.rs
+++ b/lib/rbx_loader/src/union.rs
@@ -169,8 +169,8 @@ pub fn convert(
 		});
 		polygon_groups_normal_it.chain(physics_convex_meshes_it).collect::<Result<_,_>>()?
 	}else{
-		let size=Planar64Vec3::new(size.to_array().map(|a|a.try_into().unwrap()));
-		// generate a unit cube as default physics
+		// generate a rectangular prism as default physics
+		let size=Planar64Vec3::new(size.to_array().map(|a|a.try_into().unwrap()))>>1;
 		let pos_list=CUBE_DEFAULT_VERTICES.map(|pos|
 			mb.acquire_pos_id(Planar64Vec3::new([
 				(pos.x*size.x).narrow_1().unwrap(),