diff --git a/scenes/extrudes.fart b/scenes/extrudes.fart
index 80106d4..08275c9 100644
--- a/scenes/extrudes.fart
+++ b/scenes/extrudes.fart
@@ -41,13 +41,13 @@ scene
         }
         offset 3
         material { color <1, 0.7, 0> }
-        translate <-2, 0, 0>
+        translate <-3, 0, 0>
     }
 
     extrude
     {
         ngon 5, 2
         offset 1
-        translate <2, 0, 0>
+        translate <4, 0, 0>
     }
 }
diff --git a/shapes/Extrude.cc b/shapes/Extrude.cc
index 04d9dde..6bf5ebc 100644
--- a/shapes/Extrude.cc
+++ b/shapes/Extrude.cc
@@ -35,33 +35,41 @@ Shape::IntersectionList Extrude::intersect(refptr<Shape> _this, const Ray & ray)
 {
     Ray ray_inv = m_inverse.transform_ray(ray);
     IntersectionList res;
+    int n_polygons = m_polygons.size();
+    int n_offsets = m_offsets.size();
 
-    int n_polygons = m_polygons.size(), n_offsets = m_offsets.size();
+    if (n_polygons < 1 || n_offsets < 1)
+        return res;
+
+    double distance = 0.0;
+    Vector scale(1.0, 1.0, 1.0);
+    Vector shift(0.0, 0.0, 0.0);
     for (int p = 0; p < n_polygons; p++)
     {
         refptr<Polygon> polygon = m_polygons[p];
-        double distance = 0.0;
-        Vector scale(1.0, 1.0, 1.0);
-        Vector shift(0.0, 0.0, 0.0);
         for (int o = 0; o < n_offsets; o++)
         {
             Offset & offset = m_offsets[o];
             for (int pt = 0, n_pts = polygon->size(); pt < n_pts; pt++)
             {
-                Vector p1 = *(*polygon)[pt] * scale + shift;
-                Vector p2 = *(*polygon)[(pt+1) % n_pts] * scale + shift;
-                Vector p3 = *(*polygon)[(pt+1) % n_pts]
-                    * offset.scale + offset.shift;
-                Vector p4 = *(*polygon)[pt] * offset.scale + offset.shift;
-                p3[2] += offset.distance;
-                p4[2] += offset.distance;
+                Vector p1 = scale.mult(*(*polygon)[pt]) + shift;
+                Vector p2 = scale.mult(*(*polygon)[(pt+1) % n_pts]) + shift;
+                Vector p3 = scale.mult(offset.scale)
+                    .mult(*(*polygon)[(pt+1) % n_pts])
+                    + shift + offset.shift;
+                Vector p4 = scale.mult(offset.scale).mult(*(*polygon)[pt])
+                    + shift + offset.shift;
+                p1[2] += distance;
+                p2[2] += distance;
+                p3[2] += distance + offset.distance;
+                p4[2] += distance + offset.distance;
                 Vector e1 = p2 - p1;
                 Vector e2 = p3 - p2;
                 Vector normal = (e1 * e2).normalize();
-                double a = normal[0], b = normal[1], c = normal[2];
-                double d = -a * p1[0] - b * p1[1] - c * p1[2];
                 if (ray_inv.getDirection() % normal < 0) /* skip backfaces */
                 {
+                    double a = normal[0], b = normal[1], c = normal[2];
+                    double d = -(a * p1[0] + b * p1[1] + c * p1[2]);
                     LinearSolver solver(  a * ray_inv.getDirection()[0]
                                         + b * ray_inv.getDirection()[1]
                                         + c * ray_inv.getDirection()[2],
@@ -85,8 +93,70 @@ Shape::IntersectionList Extrude::intersect(refptr<Shape> _this, const Ray & ray)
                 }
             }
             distance += offset.distance;
-            scale = offset.scale;
-            shift = offset.shift;
+            scale = scale.mult(offset.scale);
+            shift += offset.shift;
+        }
+    }
+
+    double a = 0, b = 0, c = -1.0, d = 0.0;
+    if (ray_inv.getDirection() % Vector(a, b, c) < 0)
+    {
+        LinearSolver solver(  a * ray_inv.getDirection()[0]
+                            + b * ray_inv.getDirection()[1]
+                            + c * ray_inv.getDirection()[2],
+                              a * ray_inv.getOrigin()[0]
+                            + b * ray_inv.getOrigin()[1]
+                            + c * ray_inv.getOrigin()[2]
+                            + d);
+        Solver::Result solutions = solver.solve();
+        if (solutions.numResults > 0 && solutions.results[0] > 0.0)
+        {
+            Vector ipoint = ray_inv[solutions.results[0]];
+            for (int p = 0; p < n_polygons; p++)
+            {
+                refptr<Polygon> polygon = m_polygons[p];
+                if (polygon->containsPoint(ipoint))
+                {
+                    res.add(Intersection(_this,
+                                m_transform.transform_point(ipoint),
+                                m_transform.transform_normal(Vector(a, b, c))));
+                }
+            }
+        }
+    }
+    if (scale[0] > 0.0 && scale[1] > 0.0)
+    {
+        a = 0, b = 0, c = 1.0, d = distance;
+        if (ray_inv.getDirection() % Vector(a, b, c) < 0)
+        {
+            LinearSolver solver(  a * ray_inv.getDirection()[0]
+                                + b * ray_inv.getDirection()[1]
+                                + c * ray_inv.getDirection()[2],
+                                  a * ray_inv.getOrigin()[0]
+                                + b * ray_inv.getOrigin()[1]
+                                + c * ray_inv.getOrigin()[2]
+                                + d);
+            Solver::Result solutions = solver.solve();
+            if (solutions.numResults > 0 && solutions.results[0] > 0.0)
+            {
+                Vector ipoint = ray_inv[solutions.results[0]];
+                for (int p = 0; p < n_polygons; p++)
+                {
+                    Polygon tp = *m_polygons[p];
+                    for (int i = 0, sz = tp.size(); i < sz; i++)
+                    {
+                        tp[i] = new Vector(tp[i]->mult(scale) + shift);
+                        (*tp[i])[2] += distance;
+                    }
+                    if (tp.containsPoint(ipoint))
+                    {
+                        res.add(Intersection(_this,
+                                    m_transform.transform_point(ipoint),
+                                    m_transform.transform_normal(Vector(a, b, c))));
+                        break;
+                    }
+                }
+            }
         }
     }