diff --git a/mesh/slice_triangles.m b/mesh/slice_triangles.m
index cf7b64d7..5de14f8a 100644
--- a/mesh/slice_triangles.m
+++ b/mesh/slice_triangles.m
@@ -34,6 +34,6 @@
   W = W(:,2:4);
   R = sign(sum(W.*N,2))>0;
   E(R,:) = fliplr(E(R,:));
-  E = unique(E,'rows');
-
+  [E, perm] = unique(E,'rows');
+  J = J(perm);
 end