diff --git a/src/libslic3r/ContourZ.cpp b/src/libslic3r/ContourZ.cpp
index 50a3417c22..f4a5fc049a 100644
--- a/src/libslic3r/ContourZ.cpp
+++ b/src/libslic3r/ContourZ.cpp
@@ -37,7 +37,7 @@ static bool contour_extrusion_path(LayerRegion *region, const sla::IndexedMesh &
 	}
 	
 	Layer *layer = region->layer();
-	coordf_t mesh_z = layer->print_z + mesh.ground_level();
+	coordf_t mesh_slice_z = layer->slice_z + mesh.ground_level();
 	coordf_t min_z = region->region().config().zaa_min_z;
 
 	const Points3 &points = path.polyline.points;
@@ -74,14 +74,10 @@ static bool contour_extrusion_path(LayerRegion *region, const sla::IndexedMesh &
             coordf_t x = p.x();
 			coordf_t y = p.y();
 
-			sla::IndexedMesh::hit_result hit_up = mesh.query_ray_hit({x, y, mesh_z}, {0.0, 0.0, 1.0});
-			sla::IndexedMesh::hit_result hit_down = mesh.query_ray_hit({x, y, mesh_z}, {0.0, 0.0, -1.0});
+			sla::IndexedMesh::hit_result hit_up = mesh.query_ray_hit({x, y, mesh_slice_z}, {0.0, 0.0, 1.0});
+
+			double d = hit_up.distance() - (layer->print_z - layer->slice_z);
 
-			double up = hit_up.distance();
-			double down = hit_down.distance();
-			double d = up < down ? up : -down;
-			const Vec3d &normal = (up < down ? hit_up : hit_down).normal();
-			
 			double max_up = min_z;
 			double min_down = -(height - min_z);
 			double half_width = path.width / 2.0;
@@ -90,7 +86,8 @@ static bool contour_extrusion_path(LayerRegion *region, const sla::IndexedMesh &
 				min_down = -(height + 0.1);
 			}
 
-            if (is_perimeter(path.role())) {
+            if (is_perimeter(path.role()) && hit_up.is_hit()) {
+				const Vec3d &normal = hit_up.normal();
                 double slope_rad     = slope_from_normal(normal);
                 double slope_degrees = slope_rad * 180.0 / M_PI;