diff --git a/index.html b/index.html
index 28cf377ef909c6171773cf2167c8aba5a5ee5df5..635a3f213690bdab1d514aef75aab4bbea3866a7 100755
--- a/index.html
+++ b/index.html
@@ -293,6 +293,9 @@
                 float lengthAC = length(ac);
                 float lengthBC = length(bc);
 
+                float tol = 0.0000001;
+                if (abs(lengthAB) < tol || abs(lengthBC) < tol || abs(lengthAC) < tol) continue;
+
                 ab /= lengthAB;
                 ac /= lengthAC;
                 bc /= lengthBC;