diff --git a/MarchingCubes.cpp b/MarchingCubes.cpp
index c46f936..ea91bc1 100644
--- a/MarchingCubes.cpp
+++ b/MarchingCubes.cpp
@@ -2,6 +2,8 @@
 
 #include <cassert>
 
+#include "GL/gl.h"
+
 MarchingCubes::MarchingCubes(
         const ImplicitSurface& surface,
         const Cuboid& box,
@@ -86,8 +88,24 @@ bool MarchingCubes::march_at(double x, double y, double z, Mesh& output) {
         };
 
         size_t vert_ids[3];
-        for(int i=0; i < 3; ++i)
+        for(int i=0; i < 3; ++i) {
+#ifdef DEBUG_DISPLAY_NORMAL
+            Point locVert = verts[i] + surface.getCenter();
+            Point normal = surface.normal_at(verts[i]);
+            Point outwards = locVert + normal;
+            Point inwards = locVert + ((-0.2) * normal);
+            glBegin(GL_LINES);
+                glColor3f(1., 0., 0.);
+                glVertex3f(locVert[0], locVert[1], locVert[2]);
+                glVertex3f(outwards[0], outwards[1], outwards[2]);
+                glColor3f(0., 0., 1.);
+                glVertex3f(locVert[0], locVert[1], locVert[2]);
+                glVertex3f(inwards[0], inwards[1], inwards[2]);
+            glEnd();
+#endif // DEBUG_DISPLAY_NORMAL
+
             vert_ids[i] = output.add_vertice(verts[i]);
+        }
 
         for(int i=0; i < 3; ++i) {
             output.add_face(