diff --git a/src/mode/cam/topo.js b/src/mode/cam/topo.js
index bca9ba45..9386fa17 100644
--- a/src/mode/cam/topo.js
+++ b/src/mode/cam/topo.js
@@ -354,7 +354,9 @@
                 ondone(newslices);
             }
 
-            let slicer = new KIRI.slicer2(widget.getPoints(), { swapX: true });
+            let slicer = new KIRI.slicer2(widget.getPoints(), {
+                swapX: true, emptyok: true, notopok: true
+            });
             let sindex = slicer.interval(resolution);
             stepsTotal += sindex.length * 2;
             if (proc.camContourXOn) stepsTotal += (maxX-minX) / toolStep;