diff --git a/lib/event.js b/lib/event.js
index b41d826..0214ca0 100644
--- a/lib/event.js
+++ b/lib/event.js
@@ -74,39 +74,47 @@
       _flag: {
         configurable: false,
         enumerable: false,
-        value: Object.create(Object.prototype, {
-          canceled: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          dispatch: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          initialized: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          stopImmediatePropagation: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          stopPropagation: {
+        get: function getter() {
+          var flag = Object.create(Object.prototype, {
+            canceled: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            dispatch: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            initialized: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            stopImmediatePropagation: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            stopPropagation: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            }
+          });
+          Object.defineProperty(this, '_flag', {
             configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          }
-        }),
-        writable: false
+            enumerable: false,
+            value: flag,
+            writable: false
+          });
+          return flag;
+        }
       },
       bubbles: {
         configurable: true,
diff --git a/lib/xmlhttprequest.js b/lib/xmlhttprequest.js
index c8ff8e7..f012e77 100644
--- a/lib/xmlhttprequest.js
+++ b/lib/xmlhttprequest.js
@@ -99,33 +99,41 @@
       _flag: {
         configurable: false,
         enumerable: false,
-        value: Object.create(Object.prototype, {
-          anonymous: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          synchronous: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          uploadComplete: {
-            configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          },
-          uploadEvents: {
+        get: function getter() {
+          var flag = Object.create(Object.prototype, {
+            anonymous: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            synchronous: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            uploadComplete: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            },
+            uploadEvents: {
+              configurable: false,
+              enumerable: true,
+              value: false,
+              writable: true
+            }
+          });
+          Object.defineProperty(this, '_flag', {
             configurable: false,
-            enumerable: true,
-            value: false,
-            writable: true
-          }
-        }),
-        writable: false
+            enumerable: false,
+            value: flag,
+            writable: false
+          });
+          return flag;
+        }
       },
       _properties: {
         configurable: false,