diff --git a/packages/builder/scripts/jestSetup.js b/packages/builder/scripts/jestSetup.js
index 52053d4092..ed2b7da3fd 100644
--- a/packages/builder/scripts/jestSetup.js
+++ b/packages/builder/scripts/jestSetup.js
@@ -1,3 +1,4 @@
+// Array.flat needs polyfilled in < Node 11
 if (!Array.prototype.flat) {
   Object.defineProperty(Array.prototype, "flat", {
     configurable: true,