diff --git a/src/kiri/mode/cam/work/op-area.js b/src/kiri/mode/cam/work/op-area.js
index 03a4a9fe..af080a10 100644
--- a/src/kiri/mode/cam/work/op-area.js
+++ b/src/kiri/mode/cam/work/op-area.js
@@ -134,6 +134,10 @@ class OpArea extends CamOp {
             polys = POLY.union(nupolys, 0.00001, true);
         }
 
+        // filter out invalid polys
+        polys = polys.filter(p => p && p.length > 2);
+        console.log({ polys });
+
         // process each area separately
         let proc = 0;
         let pinc = 1 / polys.length;