diff --git a/src/async.js b/src/async.js
index bf08ffb4a..2f5a49569 100644
--- a/src/async.js
+++ b/src/async.js
@@ -7,6 +7,7 @@ var Queue = require("./queue");
 var util = require("./util");
 
 function Async() {
+    this._customScheduler = false;
     this._isTickUsed = false;
     this._lateQueue = new Queue(LATE_QUEUE_CAPACITY);
     this._normalQueue = new Queue(NORMAL_QUEUE_CAPACITY);
@@ -19,6 +20,17 @@ function Async() {
     this._schedule = schedule;
 }
 
+Async.prototype.setScheduler = function(fn) {
+    var prev = this._schedule;
+    this._schedule = fn;
+    this._customScheduler = true;
+    return prev;
+};
+
+Async.prototype.hasCustomScheduler = function() {
+    return this._customScheduler;
+};
+
 Async.prototype.enableTrampoline = function() {
     this._trampolineEnabled = true;
 };
diff --git a/src/promise.js b/src/promise.js
index bad586a52..42f38d0e1 100644
--- a/src/promise.js
+++ b/src/promise.js
@@ -210,9 +210,7 @@ Promise.setScheduler = function(fn) {
     if (typeof fn !== "function") {
         throw new TypeError(FUNCTION_ERROR + util.classString(fn));
     }
-    var prev = async._schedule;
-    async._schedule = fn;
-    return prev;
+    return async.setScheduler(fn);
 };
 
 Promise.prototype._then = function (
@@ -324,6 +322,7 @@ Promise.prototype._setCancelled = function() {
 };
 
 Promise.prototype._setAsyncGuaranteed = function() {
+    if (async.hasCustomScheduler()) return;
     this._bitField = this._bitField | IS_ASYNC_GUARANTEED;
 };
 
diff --git a/test/mocha/promisify.js b/test/mocha/promisify.js
index 6e99929b6..87b1b7664 100644
--- a/test/mocha/promisify.js
+++ b/test/mocha/promisify.js
@@ -1092,3 +1092,25 @@ describe("github 1063", function() {
         });
     })
 });
+
+describe("github 1023", function() {
+    specify("promisify triggers custom schedulers", function() {
+        var triggered = false;
+        var defaultScheduler = Promise.setScheduler(function(fn) {
+            triggered = true;
+            setTimeout(fn, 0);
+        });
+        var fnAsync = Promise.promisify(function(cb) {
+            setTimeout(function() {
+                cb(null, true);
+            }, 0);
+        });
+
+        return fnAsync().then(function(result) {
+            assert(result);
+            assert(triggered);
+        }).lastly(function() {
+            Promise.setScheduler(defaultScheduler);
+        });
+    });
+})