diff --git a/src/debuggability.js b/src/debuggability.js
index 8a97eab68..024892f0a 100644
--- a/src/debuggability.js
+++ b/src/debuggability.js
@@ -4,6 +4,7 @@ var getDomain = Promise._getDomain;
 var async = Promise._async;
 var Warning = require("./errors").Warning;
 var util = require("./util");
+var es5 = require("./es5");
 var ASSERT = require("./assert");
 var canAttachTrace = util.canAttachTrace;
 var unhandledRejectionHandled;
@@ -154,10 +155,14 @@ var fireDomEvent = (function() {
             var event = new CustomEvent("CustomEvent");
             util.global.dispatchEvent(event);
             return function(name, event) {
-                var domEvent = new CustomEvent(name.toLowerCase(), {
+                var eventData = {
                     detail: event,
                     cancelable: true
-                });
+                };
+                es5.defineProperty(
+                    eventData, "promise", {value: event.promise});
+                es5.defineProperty(eventData, "reason", {value: event.reason});
+                var domEvent = new CustomEvent(name.toLowerCase(), eventData);
                 return !util.global.dispatchEvent(domEvent);
             };
         // In Firefox < 48 CustomEvent is not available in workers but
@@ -170,6 +175,8 @@ var fireDomEvent = (function() {
                     cancelable: true
                 });
                 domEvent.detail = event;
+                es5.defineProperty(domEvent, "promise", {value: event.promise});
+                es5.defineProperty(domEvent, "reason", {value: event.reason});
                 return !util.global.dispatchEvent(domEvent);
             };
         } else {
diff --git a/test/mocha/unhandled_rejections.js b/test/mocha/unhandled_rejections.js
index cf36add80..b4a43ece7 100644
--- a/test/mocha/unhandled_rejections.js
+++ b/test/mocha/unhandled_rejections.js
@@ -644,11 +644,15 @@ if (windowDomEventSupported) {
                     e.preventDefault();
                     assert.strictEqual(e.detail.promise, promise);
                     assert.strictEqual(e.detail.reason, err);
+                    assert.strictEqual(e.promise, promise);
+                    assert.strictEqual(e.reason, err);
                     order.push(1);
                 });
                 attachEvent("unhandledrejection", function(e) {
                     assert.strictEqual(e.detail.promise, promise);
                     assert.strictEqual(e.detail.reason, err);
+                    assert.strictEqual(e.promise, promise);
+                    assert.strictEqual(e.reason, err);
                     assert.strictEqual(e.defaultPrevented, true);
                     order.push(2);
                 });
@@ -656,11 +660,15 @@ if (windowDomEventSupported) {
                     e.preventDefault();
                     assert.strictEqual(e.detail.promise, promise);
                     assert.strictEqual(e.detail.reason, undefined);
+                    assert.strictEqual(e.promise, promise);
+                    assert.strictEqual(e.reason, err);
                     order.push(3);
                 });
                 attachEvent("rejectionhandled", function(e) {
                     assert.strictEqual(e.detail.promise, promise);
                     assert.strictEqual(e.detail.reason, undefined);
+                    assert.strictEqual(e.promise, promise);
+                    assert.strictEqual(e.reason, err);
                     assert.strictEqual(e.defaultPrevented, true);
                     order.push(4);
                     resolve();