diff --git a/packages/babel-helpers/src/helpers.js b/packages/babel-helpers/src/helpers.js
index 462f60a06cf4..53c78fa5110a 100644
--- a/packages/babel-helpers/src/helpers.js
+++ b/packages/babel-helpers/src/helpers.js
@@ -409,6 +409,10 @@ helpers.objectSpread = helper("7.0.0-beta.0")`
 helpers.objectSpread2 = helper("7.5.0")`
   import defineProperty from "defineProperty";
 
+  // This function is different to "Reflect.ownKeys". The enumerableOnly
+  // filters on symbol properties only. Return value always include enumerable 
+  // string properties. It is good to use in objectSpread.
+
   function ownKeys(object, enumerableOnly) {
     var keys = Object.keys(object);
     if (Object.getOwnPropertySymbols) {