diff --git a/src/12.datetimeformat.js b/src/12.datetimeformat.js
index 4ca8666b..371ab1e0 100644
--- a/src/12.datetimeformat.js
+++ b/src/12.datetimeformat.js
@@ -789,11 +789,6 @@ defineProperty(Intl.DateTimeFormat, 'supportedLocalesOf', {
     get: GetFormatDateTime
 });
 
-defineProperty(Intl.DateTimeFormat.prototype, 'formatToParts', {
-    configurable: true,
-    get: GetFormatToPartsDateTime
-});
-
 function GetFormatDateTime() {
     let internal = this !== null && typeof this === 'object' && getInternalProperties(this);
 
@@ -836,7 +831,7 @@ function GetFormatDateTime() {
     return internal['[[boundFormat]]'];
 }
 
-function GetFormatToPartsDateTime() {
+Intl.DateTimeFormat.prototype.formatToParts = function formatToParts() {
     let internal = this !== null && typeof this === 'object' && getInternalProperties(this);
 
     if (!internal || !internal['[[initializedDateTimeFormat]]'])
@@ -851,7 +846,7 @@ function GetFormatToPartsDateTime() {
         internal['[[boundFormatToParts]]'] = bf;
     }
     return internal['[[boundFormatToParts]]'];
-}
+};
 
 function CreateDateTimeParts(dateTimeFormat, x) {
     // 1. If x is not a finite Number, then throw a RangeError exception.
diff --git a/src/util.js b/src/util.js
index 40a83f2c..23ef78f8 100644
--- a/src/util.js
+++ b/src/util.js
@@ -1,8 +1,12 @@
 const realDefineProp = (function () {
         let sentinel = {};
         try {
-            Object.defineProperty(sentinel, 'a', {});
-            return 'a' in sentinel;
+            Object.defineProperty(sentinel, 'a', {
+                get: function () {
+                    return 1;
+                }
+            });
+            return sentinel.a === 1;
         } catch (e) {
             return false;
         }