diff --git a/src/util.js b/src/util.js
index 49c923cf6..12ac9b2e3 100644
--- a/src/util.js
+++ b/src/util.js
@@ -34,4 +34,21 @@ exports.isObject = function (obj) {
 
 exports.isArray = function (obj) {
   return Array.isArray(obj)
+}
+
+/**
+ * Define a readonly, in-enumerable property
+ *
+ * @param {Object} obj
+ * @param {String} key
+ * @param {*} val
+ */
+
+exports.define = function (obj, key, val) {
+  Object.defineProperty(obj, key, {
+    value: val,
+    enumerable: false,
+    writable: false,
+    configurable: true
+  })
 }
\ No newline at end of file