diff --git a/src/integer.rs b/src/integer.rs
index 46d2d67..ff16b84 100644
--- a/src/integer.rs
+++ b/src/integer.rs
@@ -653,8 +653,10 @@ impl Planar64Vec3{
 		))
 	}
 	#[inline]
-	pub fn slope(&self,up:Self)->Planar64{
-		self.dot(up)/self.cross(up).length()
+	pub fn slope_cmp(&self,slope:Planar64,up:Self)->bool{
+		let y=self.dot(up);
+		let x=self.cross(up).length();
+		y<x*slope
 	}
 	#[inline]
 	pub fn length(&self)->Planar64{
diff --git a/src/physics.rs b/src/physics.rs
index 3281baf..51084e5 100644
--- a/src/physics.rs
+++ b/src/physics.rs
@@ -1235,7 +1235,7 @@ impl crate::instruction::InstructionConsumer<PhysicsInstruction> for PhysicsStat
 								self.touching.constrain_acceleration(&self.models,&mut a);
 								self.body.acceleration=a;
 							}
-							None=>if self.style.surf_slope.map_or(true,|s|s<self.models.mesh(model_id).face_nd(c.face_id().unwrap()).0.slope(Planar64Vec3::Y)){
+							None=>if self.style.surf_slope.map_or(true,|s|self.models.mesh(model_id).face_nd(c.face_id().unwrap()).0.slope_cmp(s,Planar64Vec3::Y)){
 								//ground
 								let mut target_velocity=self.style.get_walk_target_velocity(&self.camera,self.controls,&self.next_mouse,self.time);
 								self.touching.constrain_velocity(&self.models,&mut target_velocity);