diff --git a/Tone/core/Offline.js b/Tone/core/Offline.js
index 6d2727fb..340a9a2a 100644
--- a/Tone/core/Offline.js
+++ b/Tone/core/Offline.js
@@ -66,7 +66,7 @@ define(["Tone/core/Tone", "Tone/core/Transport", "Tone/core/Buffer", "Tone/core/
 		var context = renderRet.context;
 
 		var ret;
-		if (response instanceof Promise){
+		if (response && Tone.isFunction(response.then)){
 			//wait for the promise to resolve
 			ret = response.then(function(){
 				//then render the audio
diff --git a/Tone/shim/AudioContext.js b/Tone/shim/AudioContext.js
index 4ef7d8ff..118a563e 100644
--- a/Tone/shim/AudioContext.js
+++ b/Tone/shim/AudioContext.js
@@ -40,7 +40,7 @@ define(["Tone/core/Tone", "Tone/shim/OfflineAudioContext"], function(Tone){
 		var audioData = new Uint32Array([1179011410, 48, 1163280727, 544501094, 16, 131073, 44100, 176400, 1048580, 1635017060, 8, 0, 0, 0, 0]).buffer;
 		try {
 			var ret = offlineContext.decodeAudioData(audioData);
-			if (ret instanceof Promise){
+			if (ret && Tone.isFunction(ret.then)){
 				decodeAudioDataPromise = true;
 			}
 		} catch (e){
diff --git a/Tone/shim/OfflineAudioContext.js b/Tone/shim/OfflineAudioContext.js
index 91b63816..161c7f02 100644
--- a/Tone/shim/OfflineAudioContext.js
+++ b/Tone/shim/OfflineAudioContext.js
@@ -8,7 +8,7 @@ define(["Tone/core/Tone"], function(Tone){
 		//returns promise?
 		var context = new OfflineAudioContext(1, 1, 44100);
 		var ret = context.startRendering();
-		if (!(ret instanceof Promise)){
+		if (!(ret && Tone.isFunction(ret.then))){
 			OfflineAudioContext.prototype._native_startRendering = OfflineAudioContext.prototype.startRendering;
 			OfflineAudioContext.prototype.startRendering = function(){
 				return new Promise(function(done){
diff --git a/test/helper/Offline.js b/test/helper/Offline.js
index 572ea21e..7542ad7c 100644
--- a/test/helper/Offline.js
+++ b/test/helper/Offline.js
@@ -1,24 +1,23 @@
-define(["Tone/core/Tone", "Tone/core/Offline", "helper/BufferTest", "Tone/core/Master"],
-	function(Tone, Offline, BufferTest, Master) {
+define(["Tone/core/Tone", "Tone/core/Offline", "helper/BufferTest", "Tone/core/Master"], function(Tone, Offline, BufferTest, Master){
 
-		return function(callback, duration, channels){
-			duration = duration || 0.1;
-			channels = channels || 1;
-			return Offline(function(Transport){
-				var testFn = callback(Transport);
-				if (testFn instanceof Promise){
-					return testFn;
-				} else if (Tone.isFunction(testFn)){
-					Transport.context.on("tick", function(){
-						testFn(Transport.now());
-					});
-				}
-			}, duration).then(function(buffer){
-				BufferTest(buffer);
-				if (channels === 1){
-					buffer.toMono();
-				}
-				return buffer;
-			});
-		};
-	});
+	return function(callback, duration, channels){
+		duration = duration || 0.1;
+		channels = channels || 1;
+		return Offline(function(Transport){
+			var testFn = callback(Transport);
+			if (testFn && Tone.isFunction(testFn.then)){
+				return testFn;
+			} else if (Tone.isFunction(testFn)){
+				Transport.context.on("tick", function(){
+					testFn(Transport.now());
+				});
+			}
+		}, duration).then(function(buffer){
+			BufferTest(buffer);
+			if (channels === 1){
+				buffer.toMono();
+			}
+			return buffer;
+		});
+	};
+});