diff --git a/src/model_physics.rs b/src/model_physics.rs
index 87a44c2..6c1cbbb 100644
--- a/src/model_physics.rs
+++ b/src/model_physics.rs
@@ -969,7 +969,7 @@ fn is_empty_volume(normals:Vec<Vector3<Fixed<3,96>>>)->bool{
 				if k!=i&&k!=j{
 					let d=n.dot(normals[k]);
 					if let Some(comp)=&d_comp{
-						if comp.is_negative()&&d.is_negative()||comp.is_positive()&&d.is_positive(){
+						if comp.is_negative()^d.is_negative(){
 							return true;
 						}
 					}else{