diff --git a/shader/dualTwoD/ellipse.vert b/shader/dualTwoD/ellipse.vert
index 67e6c0c68..57be8e0c2 100644
--- a/shader/dualTwoD/ellipse.vert
+++ b/shader/dualTwoD/ellipse.vert
@@ -20,7 +20,7 @@ const vec2 bs[4] =
     } ;
 void main()
 {
-    int i0 = n + (3 * (gl_VertexID/6) );
+    int i0 = n + (3 * ((gl_VertexID-n)/6) );
     gColC = data[i0].colx;
     gColE = data[i0+1].colx;
     int k = ks[gl_VertexID % 6];