diff --git a/src/kiri/mode/cam/work/op-contour.js b/src/kiri/mode/cam/work/op-contour.js
index e51ce6bd..7bcf7c8f 100644
--- a/src/kiri/mode/cam/work/op-contour.js
+++ b/src/kiri/mode/cam/work/op-contour.js
@@ -21,7 +21,7 @@ function createFilter(op, origin, axis) {
             let index = 0;
             const accept = [];
             filter = function (slices) {
-                for (let slice of slices) {
+                for (let slice of slices.filter(s => s.camLines)) {
                     if (slice_fn && slice_fn(slice, index++)) {
                         accept.push(slice);
                     } else if (box) {