diff --git a/render/GlutRender.cpp b/render/GlutRender.cpp
index cedf0c5..4e8742c 100644
--- a/render/GlutRender.cpp
+++ b/render/GlutRender.cpp
@@ -78,7 +78,7 @@ void GlutRender::reshape(int wid, int hei) {
     gluPerspective(45.0f, aspect, 0.1f, 100.0f);
 }
 
-void GlutRender::display_mesh(const Mesh& mesh) const {
+void GlutRender::display_mesh(Mesh& mesh) const {
     const Point& mesh_center = mesh.get_center();
 
     const std::vector<Point>& points = mesh.get_vertices();
@@ -88,10 +88,15 @@ void GlutRender::display_mesh(const Mesh& mesh) const {
         Point p0 = face.pt(0, points) + mesh_center,
               p1 = face.pt(1, points) + mesh_center,
               p2 = face.pt(2, points) + mesh_center;
+        Point n0 = mesh.get_normal(face[0]),
+              n1 = mesh.get_normal(face[1]),
+              n2 = mesh.get_normal(face[2]);
+
         glColor3f(rand_color(), rand_color(), rand_color());
-        glVertex3f(p0[0], p0[1], p0[2]);
-        glVertex3f(p1[0], p1[1], p1[2]);
-        glVertex3f(p2[0], p2[1], p2[2]);
+
+        glNormal3f(n0[0], n0[1], n0[2]); glVertex3f(p0[0], p0[1], p0[2]);
+        glNormal3f(n1[0], n1[1], n1[2]); glVertex3f(p1[0], p1[1], p1[2]);
+        glNormal3f(n2[0], n2[1], n2[2]); glVertex3f(p2[0], p2[1], p2[2]);
     }
     glEnd();
 }