diff --git a/docs/chapters/offsetting/offsetting.js b/docs/chapters/offsetting/offsetting.js
index 8166c886..a455932e 100644
--- a/docs/chapters/offsetting/offsetting.js
+++ b/docs/chapters/offsetting/offsetting.js
@@ -72,6 +72,7 @@ reduce(curve) {
     pass2 = [];
 
   // first pass: split on extrema
+  curve.verify();
   let extrema = curve.extrema().values;
   if (extrema.indexOf(0) === -1) {
     extrema = [0].concat(extrema);