diff --git a/web/app/3d/craft/brep/wizards/cut-extrude.js b/web/app/3d/craft/brep/wizards/cut-extrude.js
index 22d562ca..17893537 100644
--- a/web/app/3d/craft/brep/wizards/cut-extrude.js
+++ b/web/app/3d/craft/brep/wizards/cut-extrude.js
@@ -1,6 +1,8 @@
 import {CURRENT_SELECTION as S} from './wizard'
 import {PreviewWizard, SketchBasedPreviewer} from './preview-wizard'
 import {ParametricExtruder, fixNegativeValue} from '../cut-extrude'
+import {TriangulatePolygons} from '../../../triangulation'
+import Vector from '../../../../math/vector'
 
 const METADATA = [
   ['value'   , 'number',  50],
@@ -68,6 +70,11 @@ export class ExtrudePreviewer extends SketchBasedPreviewer {
         triangles.push([ base[p], base[q], lid[q] ]);
         triangles.push([ lid[q], lid[p], base[p] ]);
       }
+      TriangulatePolygons([base], baseNormal, (v) => v.toArray(), (arr) => new Vector().set3(arr))
+        .forEach(tr => triangles.push(tr));
+      
+      TriangulatePolygons([lid], lidNormal, (v) => v.toArray(), (arr) => new Vector().set3(arr))
+        .forEach(tr => triangles.push(tr));
     }
     return triangles;
   }
diff --git a/web/app/3d/scene/brep-scene-object.js b/web/app/3d/scene/brep-scene-object.js
index 674fbc0d..ef8f5c63 100644
--- a/web/app/3d/scene/brep-scene-object.js
+++ b/web/app/3d/scene/brep-scene-object.js
@@ -82,7 +82,7 @@ class BREPSceneFace extends SceneFace {
 }
 
 function triangulate(face) {
-  function csgVert(data) {
+  function v(data) {
     return new Vector(data[0], data[1], data[2]);
   }
   function data(v) {
@@ -97,13 +97,12 @@ function triangulate(face) {
 
   let vertices = Triangulate(contours, data(face.surface.normal));
   for (let i = 0;  i < vertices.length; i += 3 ) {
-    var a = csgVert(vertices[i]);
-    var b = csgVert(vertices[i + 1]);
-    var c = csgVert(vertices[i + 2]);
+    var a = v(vertices[i]);
+    var b = v(vertices[i + 1]);
+    var c = v(vertices[i + 2]);
     triangled.push([a, b, c]);
   }
   return triangled;
-
 }
 
 export function triangulateToThree(shell, geom) {    
diff --git a/web/app/3d/triangulation.js b/web/app/3d/triangulation.js
index 52961c91..00be4338 100644
--- a/web/app/3d/triangulation.js
+++ b/web/app/3d/triangulation.js
@@ -65,6 +65,23 @@ export function Triangulate(contours, normal) {
   return triangleVerts;
 }
 
+export function TriangulatePolygons(polygons, normal, toArray, fromArray) {
+  const triangled = [];
+  const contours = [];
+  for (let poly of polygons) {
+    contours.push(poly.map(point => toArray(point)));
+  }
+
+  let vertices = Triangulate(contours, toArray(normal));
+  for (let i = 0;  i < vertices.length; i += 3 ) {
+    var a = fromArray(vertices[i]);
+    var b = fromArray(vertices[i + 1]);
+    var c = fromArray(vertices[i + 2]);
+    triangled.push([a, b, c]);
+  }
+  return triangled;
+}
+
 export function TriangulateFace(face) {
   function arr(v) {
     return [v.x, v.y, v.z];
diff --git a/web/app/math/vector.js b/web/app/math/vector.js
index 3e216167..d82875f7 100644
--- a/web/app/math/vector.js
+++ b/web/app/math/vector.js
@@ -126,6 +126,10 @@ Vector.prototype.equals = function(vector) {
   return vectorsEqual(this, vector);
 };
 
+Vector.prototype.toArray = function() {
+  return [this.x, this.y, this.z];
+};
+
 Vector.prototype.three = function() {
   return new THREE.Vector3(this.x, this.y, this.z);
 };