diff --git a/async/async-tests.ts b/async/async-tests.ts
index 67df5bae09..37c561e641 100644
--- a/async/async-tests.ts
+++ b/async/async-tests.ts
@@ -1,23 +1,25 @@
 /// <reference path="async.d.ts" />
-
-var fs, path;
+/// <reference path="../node/node.d.ts" />
+import * as fs from "fs";
+// var fs = require("fs");
 
 function callback() {}
+function funcStringCbErrBoolean(v:string, cb:(err:Error,res:boolean) => void) {}
 
-async.map(['file1', 'file2', 'file3'], fs.stat, function (err, results) { });
-async.mapSeries(['file1', 'file2', 'file3'], fs.stat, function (err, results) { });
-async.mapLimit(['file1', 'file2', 'file3'], 2, fs.stat, function (err, results) { });
+async.map(['file1', 'file2', 'file3'], fs.stat, function (err:Error, results:Array<fs.Stats>) { });
+async.mapSeries(['file1', 'file2', 'file3'], fs.stat, function (err:Error, results:Array<fs.Stats>) { });
+async.mapLimit(['file1', 'file2', 'file3'], 2, fs.stat, function (err:Error, results:Array<fs.Stats>) { });
 
-async.filter(['file1', 'file2', 'file3'], path.exists, function (results) { });
-async.filterSeries(['file1', 'file2', 'file3'], path.exists, function (results) { });
-async.filterLimit(['file1', 'file2', 'file3'], 2, path.exists, function (results) { });
-async.select(['file1', 'file2', 'file3'], path.exists, function (results) { });
-async.selectSeries(['file1', 'file2', 'file3'], path.exists, function (results) { });
-async.selectLimit(['file1', 'file2', 'file3'], 2, path.exists, function (results) { });
+async.filter(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.filterSeries(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.filterLimit(['file1', 'file2', 'file3'], 2, funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.select(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.selectSeries(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.selectLimit(['file1', 'file2', 'file3'], 2, funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
 
-async.reject(['file1', 'file2', 'file3'], path.exists, function (results) { });
-async.rejectSeries(['file1', 'file2', 'file3'], path.exists, function (results) { });
-async.rejectLimit(['file1', 'file2', 'file3'], 2, path.exists, function (results) { });
+async.reject(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.rejectSeries(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
+async.rejectLimit(['file1', 'file2', 'file3'], 2, funcStringCbErrBoolean, function (err:Error,results:Array<string>) { });
 
 async.parallel([
     function () { },
@@ -41,9 +43,9 @@ var openFilesObj = {
     file2: "fileTwo"
 }
 
-var saveFile = function () { }
-async.each(openFiles, saveFile, function (err) { });
-async.eachSeries(openFiles, saveFile, function (err) { });
+var saveFile = function (file:string,cb:(err:Error)=>void) { }
+async.each(openFiles, saveFile, function (err:Error) { });
+async.eachSeries(openFiles, saveFile, function (err:Error) { });
 
 var documents, requestApi;
 async.eachLimit(documents, 20, requestApi, function (err) { });
@@ -73,9 +75,9 @@ async.foldl(numArray, 0, reducer, function (err, result) { });
 async.reduceRight(numArray, 0, reducer, function (err, result) { });
 async.foldr(numArray, 0, reducer, function (err, result) { });
 
-async.detect(['file1', 'file2', 'file3'], path.exists, function (result) { });
-async.detectSeries(['file1', 'file2', 'file3'], path.exists, function (result) { });
-async.detectLimit(['file1', 'file2', 'file3'], 2, path.exists, function (result) { });
+async.detect(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err,result:string) { });
+async.detectSeries(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err,result) { });
+async.detectLimit(['file1', 'file2', 'file3'], 2, funcStringCbErrBoolean, function (err,result) { });
 
 async.sortBy(['file1', 'file2', 'file3'], function (file, callback) {
     fs.stat(file, function (err, stats) {
@@ -83,13 +85,13 @@ async.sortBy(['file1', 'file2', 'file3'], function (file, callback) {
     });
 }, function (err, results) { });
 
-async.some(['file1', 'file2', 'file3'], path.exists, function (result) { });
-async.someLimit(['file1', 'file2', 'file3'], 2, path.exists, function (result) { });
-async.any(['file1', 'file2', 'file3'], path.exists, function (result) { });
+async.some(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,result:boolean) { });
+async.someLimit(['file1', 'file2', 'file3'], 2, funcStringCbErrBoolean, function (err:Error,result:boolean) { });
+async.any(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,result:boolean) { });
 
-async.every(['file1', 'file2', 'file3'], path.exists, function (result) { });
-async.everyLimit(['file1', 'file2', 'file3'], 2, path.exists, function (result) { });
-async.all(['file1', 'file2', 'file3'], path.exists, function (result) { });
+async.every(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,result:boolean) { });
+async.everyLimit(['file1', 'file2', 'file3'], 2, funcStringCbErrBoolean, function (err:Error,result:boolean) { });
+async.all(['file1', 'file2', 'file3'], funcStringCbErrBoolean, function (err:Error,result:boolean) { });
 
 async.concat(['dir1', 'dir2', 'dir3'], fs.readdir, function (err, files) { });
 async.concatSeries(['dir1', 'dir2', 'dir3'], fs.readdir, function (err, files) { });
@@ -107,7 +109,7 @@ async.series([
 ],
 function (err, results) { });
 
-async.series<string>([
+async.series<string,Error>([
     function (callback) {
         callback(null, 'one');
     },
@@ -131,7 +133,7 @@ async.series({
 },
 function (err, results) { });
 
-async.series<number>({
+async.series<number,Error>({
     one: function (callback) {
         setTimeout(function () {
             callback(null, 1);
@@ -171,7 +173,7 @@ async.parallel([
 ],
 function (err, results) { });
 
-async.parallel<string>([
+async.parallel<string,Error>([
     function (callback) {
         setTimeout(function () {
             callback(null, 'one');
@@ -200,7 +202,7 @@ async.parallel({
 },
 function (err, results) { });
 
-async.parallel<number>({
+async.parallel<number,Error>({
     one: function (callback) {
         setTimeout(function () {
             callback(null, 1);
@@ -266,7 +268,7 @@ async.waterfall([
 ], function (err, result) { });
 
 
-var q = async.queue<any>(function (task: any, callback) {
+var q = async.queue<any,Error>(function (task: any, callback) {
     console.log('hello ' + task.name);
     callback();
 }, 2);
@@ -319,7 +321,7 @@ q.resume();
 q.kill();
 
 // tests for strongly typed tasks
-var q2 = async.queue<string>(function (task: string, callback) {
+var q2 = async.queue<string,Error>(function (task: string, callback) {
     console.log('Task: ' + task);
     callback();
 }, 1);
@@ -382,10 +384,10 @@ async.retry({ times: 3, interval: (retryCount) => { return 200 * retryCount; } }
 
 
 async.parallel([
-    function (callback) { },
+    function (callback: ( err:Error, val:string ) => void ) { },
     function (callback) { }
 ],
-function (results) {
+function (err:Error,results:Array<string>) {
     async.series([
         function (callback) { },
         function email_link(callback) { }
@@ -438,10 +440,10 @@ async.dir(function (name, callback) {
 
 // each
 
-async.each<number>({
+async.each<number,Error>({
     "a": 1,
     "b": 2
-}, function(val: number, next: ErrorCallback): void {
+}, function(val: number, next: ErrorCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -457,10 +459,10 @@ async.each<number>({
 
 });
 
-async.eachSeries<number>({
+async.eachSeries<number, Error>({
     "a": 1,
     "b": 2
-}, function(val: number, next: ErrorCallback): void {
+}, function(val: number, next: ErrorCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -476,14 +478,14 @@ async.eachSeries<number>({
 
 });
 
-async.eachLimit<number>({
+async.eachLimit<number, Error>({
     "a": 1,
     "b": 2,
     "c": 3,
     "d": 4,
     "e": 5,
     "f": 6
-}, 2, function(val: number, next: ErrorCallback): void {
+}, 2, function(val: number, next: ErrorCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -501,10 +503,10 @@ async.eachLimit<number>({
 
 // forEachOf/eachOf
 
-async.eachOf<number>({
+async.eachOf<number, Error>({
     "a": 1,
     "b": 2
-}, function(val: number, key: string, next: ErrorCallback): void {
+}, function(val: number, key: string, next: ErrorCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -520,10 +522,10 @@ async.eachOf<number>({
 
 });
 
-async.forEachOfSeries<number>({
+async.forEachOfSeries<number, Error>({
     "a": 1,
     "b": 2
-}, function(val: number, key: string, next: ErrorCallback): void {
+}, function(val: number, key: string, next: ErrorCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -539,14 +541,14 @@ async.forEachOfSeries<number>({
 
 });
 
-async.forEachOfLimit<number>({
+async.forEachOfLimit<number, Error>({
     "a": 1,
     "b": 2,
     "c": 3,
     "d": 4,
     "e": 5,
     "f": 6
-}, 2, function(val: number, key: string, next: ErrorCallback): void {
+}, 2, function(val: number, key: string, next: ErrorCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -564,11 +566,11 @@ async.forEachOfLimit<number>({
 
 // map
 
-async.map<number, string>({
+async.map<number, string, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(val: number, next: AsyncResultCallback<string>): void {
+}, function(val: number, next: AsyncResultCallback<string, Error>): void {
 
     setTimeout(function(): void {
 
@@ -584,11 +586,11 @@ async.map<number, string>({
 
 });
 
-async.mapSeries<number, string>({
+async.mapSeries<number, string, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(val: number, next: AsyncResultCallback<string>): void {
+}, function(val: number, next: AsyncResultCallback<string, Error>): void {
 
     setTimeout(function(): void {
 
@@ -604,14 +606,14 @@ async.mapSeries<number, string>({
 
 });
 
-async.mapLimit<number, string>({
+async.mapLimit<number, string, Error>({
     "a": 1,
     "b": 2,
     "c": 3,
     "d": 4,
     "e": 5,
     "f": 6
-}, 2, function(val: number, next: AsyncResultCallback<string>): void {
+}, 2, function(val: number, next: AsyncResultCallback<string, Error>): void {
 
     setTimeout(function(): void {
 
@@ -629,11 +631,11 @@ async.mapLimit<number, string>({
 
 // mapValues
 
-async.mapValues<number, string>({
+async.mapValues<number, string, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(val: number, key: string, next: AsyncResultCallback<string>): void {
+}, function(val: number, key: string, next: AsyncResultCallback<string, Error>): void {
 
     setTimeout(function(): void {
 
@@ -649,11 +651,11 @@ async.mapValues<number, string>({
 
 });
 
-async.mapValuesSeries<number, string>({
+async.mapValuesSeries<number, string, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(val: number, key: string, next: AsyncResultCallback<string>): void {
+}, function(val: number, key: string, next: AsyncResultCallback<string, Error>): void {
 
     setTimeout(function(): void {
 
@@ -671,11 +673,11 @@ async.mapValuesSeries<number, string>({
 
 // filter/select/reject
 
-async.filter<number>({
+async.filter<number, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(val: number, next: AsyncBooleanResultCallback): void {
+}, function(val: number, next: AsyncBooleanResultCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -691,11 +693,11 @@ async.filter<number>({
 
 });
 
-async.reject<number>({
+async.reject<number, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(val: number, next: AsyncBooleanResultCallback): void {
+}, function(val: number, next: AsyncBooleanResultCallback<Error>): void {
 
     setTimeout(function(): void {
 
@@ -713,11 +715,11 @@ async.reject<number>({
 
 // concat
 
-async.concat<string, string>({
+async.concat<string, string, Error>({
     "a": "1",
     "b": "2",
     "c": "3"
-}, function(item: string, next: AsyncResultCallback<string[]>): void {
+}, function(item: string, next: AsyncResultCallback<string[], Error>): void {
 
     console.log(`async.concat: ${item}`);
 
@@ -731,11 +733,11 @@ async.concat<string, string>({
 
 // detect/find
 
-async.detect<number>({
+async.detect<number, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(item: number, next: AsyncBooleanResultCallback): void {
+}, function(item: number, next: AsyncBooleanResultCallback<Error>): void {
 
     console.log(`async.detect/find: ${item}`);
 
@@ -756,11 +758,11 @@ async.detect<number>({
 
 // every/all
 
-async.every<number>({
+async.every<number,Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(item: number, next: AsyncBooleanResultCallback): void {
+}, function(item: number, next: AsyncBooleanResultCallback<Error>): void {
 
     console.log(`async.every/all: ${item}`);
 
@@ -774,11 +776,11 @@ async.every<number>({
 
 // some/any
 
-async.some<number>({
+async.some<number, Error>({
     "a": 1,
     "b": 2,
     "c": 3
-}, function(item: number, next: AsyncBooleanResultCallback): void {
+}, function(item: number, next: AsyncBooleanResultCallback<Error>): void {
 
     console.log(`async.some/any: ${item}`);
 
diff --git a/async/async.d.ts b/async/async.d.ts
index 8b564fbd80..45d39ea955 100644
--- a/async/async.d.ts
+++ b/async/async.d.ts
@@ -5,22 +5,22 @@
 
 interface Dictionary<T> { [key: string]: T; }
 
-interface ErrorCallback { (err?: Error): void; }
-interface AsyncWaterfallCallback { (err: Error, ...args: any[]): void; }
-interface AsyncBooleanResultCallback { (err: Error, truthValue: boolean): void; }
-interface AsyncResultCallback<T> { (err: Error, result: T): void; }
-interface AsyncResultArrayCallback<T> { (err: Error, results: T[]): void; }
-interface AsyncResultObjectCallback<T> { (err: Error, results: Dictionary<T>): void; }
+interface ErrorCallback<T> { (err?: T): void; }
+interface AsyncWaterfallCallback<E> { (err: E, ...args: any[]): void; }
+interface AsyncBooleanResultCallback<E> { (err: E, truthValue: boolean): void; }
+interface AsyncResultCallback<T, E> { (err: E, result: T): void; }
+interface AsyncResultArrayCallback<T, E> { (err: E, results: T[]): void; }
+interface AsyncResultObjectCallback<T, E> { (err: E, results: Dictionary<T>): void; }
 
-interface AsyncFunction<T> { (callback: (err?: Error, result?: T) => void): void; }
-interface AsyncIterator<T> { (item: T, callback: ErrorCallback): void; }
-interface AsyncForEachOfIterator<T> { (item: T, key: number|string, callback: ErrorCallback): void; }
-interface AsyncResultIterator<T, R> { (item: T, callback: AsyncResultCallback<R>): void; }
-interface AsyncMemoIterator<T, R> { (memo: R, item: T, callback: AsyncResultCallback<R>): void; }
-interface AsyncBooleanIterator<T> { (item: T, callback: AsyncBooleanResultCallback): void; }
+interface AsyncFunction<T, E> { (callback: (err?: E, result?: T) => void): void; }
+interface AsyncIterator<T, E> { (item: T, callback: ErrorCallback<E>): void; }
+interface AsyncForEachOfIterator<T, E> { (item: T, key: number|string, callback: ErrorCallback<E>): void; }
+interface AsyncResultIterator<T, R, E> { (item: T, callback: AsyncResultCallback<R, E>): void; }
+interface AsyncMemoIterator<T, R, E> { (memo: R, item: T, callback: AsyncResultCallback<R, E>): void; }
+interface AsyncBooleanIterator<T, E> { (item: T, callback: AsyncBooleanResultCallback<E>): void; }
 
-interface AsyncWorker<T> { (task: T, callback: ErrorCallback): void; }
-interface AsyncVoidFunction { (callback: ErrorCallback): void; }
+interface AsyncWorker<T, E> { (task: T, callback: ErrorCallback<E>): void; }
+interface AsyncVoidFunction<E> { (callback: ErrorCallback<E>): void; }
 
 interface AsyncQueue<T> {
     length(): number;
@@ -28,10 +28,10 @@ interface AsyncQueue<T> {
     running(): number;
     idle(): boolean;
     concurrency: number;
-    push(task: T, callback?: ErrorCallback): void;
-    push(task: T[], callback?: ErrorCallback): void;
-    unshift(task: T, callback?: ErrorCallback): void;
-    unshift(task: T[], callback?: ErrorCallback): void;
+    push<E>(task: T, callback?: ErrorCallback<E>): void;
+    push<E>(task: T[], callback?: ErrorCallback<E>): void;
+    unshift<E>(task: T, callback?: ErrorCallback<E>): void;
+    unshift<E>(task: T[], callback?: ErrorCallback<E>): void;
     saturated: () => any;
     empty: () => any;
     drain: () => any;
@@ -53,8 +53,8 @@ interface AsyncPriorityQueue<T> {
     concurrency: number;
     started: boolean;
     paused: boolean;
-    push(task: T, priority: number, callback?: AsyncResultArrayCallback<T>): void;
-    push(task: T[], priority: number, callback?: AsyncResultArrayCallback<T>): void;
+    push<E>(task: T, priority: number, callback?: AsyncResultArrayCallback<T, E>): void;
+    push<E>(task: T[], priority: number, callback?: AsyncResultArrayCallback<T, E>): void;
     saturated: () => any;
     empty: () => any;
     drain: () => any;
@@ -90,122 +90,122 @@ interface AsyncCargo {
 interface Async {
 
     // Collections
-    each<T>(arr: T[], iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
-    each<T>(arr: Dictionary<T>, iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
+    each<T, E>(arr: T[], iterator: AsyncIterator<T, E>, callback?: ErrorCallback<E>): void;
+    each<T, E>(arr: Dictionary<T>, iterator: AsyncIterator<T, E>, callback?: ErrorCallback<E>): void;
     eachSeries: typeof async.each;
-    eachLimit<T>(arr: T[], limit: number, iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
-    eachLimit<T>(arr: Dictionary<T>, limit: number, iterator: AsyncIterator<T>, callback?: ErrorCallback): void;
+    eachLimit<T, E>(arr: T[], limit: number, iterator: AsyncIterator<T, E>, callback?: ErrorCallback<E>): void;
+    eachLimit<T, E>(arr: Dictionary<T>, limit: number, iterator: AsyncIterator<T, E>, callback?: ErrorCallback<E>): void;
     forEach: typeof async.each;
     forEachSeries: typeof async.each;
     forEachLimit: typeof async.eachLimit;
-    forEachOf<T>(obj: T[], iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
-    forEachOf<T>(obj: Dictionary<T>, iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
+    forEachOf<T, E>(obj: T[], iterator: AsyncForEachOfIterator<T, E>, callback?: ErrorCallback<E>): void;
+    forEachOf<T, E>(obj: Dictionary<T>, iterator: AsyncForEachOfIterator<T, E>, callback?: ErrorCallback<E>): void;
     forEachOfSeries: typeof async.forEachOf;
-    forEachOfLimit<T>(obj: T[], limit: number, iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
-    forEachOfLimit<T>(obj: Dictionary<T>, limit: number, iterator: AsyncForEachOfIterator<T>, callback?: ErrorCallback): void;
+    forEachOfLimit<T, E>(obj: T[], limit: number, iterator: AsyncForEachOfIterator<T, E>, callback?: ErrorCallback<E>): void;
+    forEachOfLimit<T, E>(obj: Dictionary<T>, limit: number, iterator: AsyncForEachOfIterator<T, E>, callback?: ErrorCallback<E>): void;
     eachOf: typeof async.forEachOf;
     eachOfSeries: typeof async.forEachOf;
     eachOfLimit: typeof async.forEachOfLimit;
-    map<T, R>(arr: T[], iterator: AsyncResultIterator<T, R>, callback?: AsyncResultArrayCallback<R>): void;
-    map<T, R>(arr: Dictionary<T>, iterator: AsyncResultIterator<T, R>, callback?: AsyncResultArrayCallback<R>): void;
+    map<T, R, E>(arr: T[], iterator: AsyncResultIterator<T, R, E>, callback?: AsyncResultArrayCallback<R, E>): void;
+    map<T, R, E>(arr: Dictionary<T>, iterator: AsyncResultIterator<T, R, E>, callback?: AsyncResultArrayCallback<R, E>): void;
     mapSeries: typeof async.map;
-    mapLimit<T, R>(arr: T[], limit: number, iterator: AsyncResultIterator<T, R>, callback?: AsyncResultArrayCallback<R>): void;
-    mapLimit<T, R>(arr: Dictionary<T>, limit: number, iterator: AsyncResultIterator<T, R>, callback?: AsyncResultArrayCallback<R>): void;
-    mapValuesLimit<T, R>(obj: Dictionary<T>, limit: number, iteratee: (value: T, key: string, callback: AsyncResultCallback<R>) => void, callback: AsyncResultCallback<R[]>): void;
-    mapValues<T, R>(obj: Dictionary<T>, iteratee: (value: T, key: string, callback: AsyncResultCallback<R>) => void, callback: AsyncResultCallback<R[]>): void;
+    mapLimit<T, R, E>(arr: T[], limit: number, iterator: AsyncResultIterator<T, R, E>, callback?: AsyncResultArrayCallback<R, E>): void;
+    mapLimit<T, R, E>(arr: Dictionary<T>, limit: number, iterator: AsyncResultIterator<T, R, E>, callback?: AsyncResultArrayCallback<R, E>): void;
+    mapValuesLimit<T, R, E>(obj: Dictionary<T>, limit: number, iteratee: (value: T, key: string, callback: AsyncResultCallback<R, E>) => void, callback: AsyncResultCallback<R[], E>): void;
+    mapValues<T, R, E>(obj: Dictionary<T>, iteratee: (value: T, key: string, callback: AsyncResultCallback<R, E>) => void, callback: AsyncResultCallback<R[], E>): void;
     mapValuesSeries: typeof async.mapValues;
-    filter<T>(arr: T[], iterator: AsyncBooleanIterator<T>, callback?: AsyncResultArrayCallback<T>): void;
-    filter<T>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T>, callback?: AsyncResultArrayCallback<T>): void;
+    filter<T, E>(arr: T[], iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultArrayCallback<T, E>): void;
+    filter<T, E>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultArrayCallback<T, E>): void;
     filterSeries: typeof async.filter;
-    filterLimit<T>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncResultArrayCallback<T>): void;
-    filterLimit<T>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncResultArrayCallback<T>): void;
+    filterLimit<T, E>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultArrayCallback<T, E>): void;
+    filterLimit<T, E>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultArrayCallback<T, E>): void;
     select: typeof async.filter;
     selectSeries: typeof async.filter;
     selectLimit: typeof async.filterLimit;
     reject: typeof async.filter;
     rejectSeries: typeof async.filter;
     rejectLimit: typeof async.filterLimit;
-    reduce<T, R>(arr: T[], memo: R, iterator: AsyncMemoIterator<T, R>, callback?: AsyncResultCallback<R>): void;
+    reduce<T, R, E>(arr: T[], memo: R, iterator: AsyncMemoIterator<T, R, E>, callback?: AsyncResultCallback<R, E>): void;
     inject: typeof async.reduce;
     foldl: typeof async.reduce;
     reduceRight: typeof async.reduce;
     foldr: typeof async.reduce;
-    detect<T>(arr: T[], iterator: AsyncBooleanIterator<T>, callback?: AsyncResultCallback<T>): void;
-    detect<T>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T>, callback?: AsyncResultCallback<T>): void;
+    detect<T, E>(arr: T[], iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultCallback<T, E>): void;
+    detect<T, E>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultCallback<T, E>): void;
     detectSeries: typeof async.detect;
-    detectLimit<T>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncResultCallback<T>): void;
-    detectLimit<T>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncResultCallback<T>): void;
+    detectLimit<T, E>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultCallback<T, E>): void;
+    detectLimit<T, E>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncResultCallback<T, E>): void;
     find: typeof async.detect;
     findSeries: typeof async.detect;
     findLimit: typeof async.detectLimit;
-    sortBy<T, V>(arr: T[], iterator: AsyncResultIterator<T, V>, callback?: AsyncResultArrayCallback<T>): void;
-    some<T>(arr: T[], iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
-    some<T>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
+    sortBy<T, V, E>(arr: T[], iterator: AsyncResultIterator<T, V, E>, callback?: AsyncResultArrayCallback<T, E>): void;
+    some<T, E>(arr: T[], iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
+    some<T, E>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
     someSeries: typeof async.some;
-    someLimit<T>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
-    someLimit<T>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
+    someLimit<T, E>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
+    someLimit<T, E>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
     any: typeof async.some;
     anySeries: typeof async.someSeries;
     anyLimit: typeof async.someLimit;
-    every<T>(arr: T[], iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
-    every<T>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
+    every<T, E>(arr: T[], iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
+    every<T, E>(arr: Dictionary<T>, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
     everySeries: typeof async.every;
-    everyLimit<T>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
-    everyLimit<T>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T>, callback?: AsyncBooleanResultCallback): void;
+    everyLimit<T, E>(arr: T[], limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
+    everyLimit<T, E>(arr: Dictionary<T>, limit: number, iterator: AsyncBooleanIterator<T, E>, callback?: AsyncBooleanResultCallback<E>): void;
     all: typeof async.every;
     allSeries: typeof async.every;
     allLimit: typeof async.everyLimit;
 
-    concat<T, R>(arr: T[], iterator: AsyncResultIterator<T, R[]>, callback?: AsyncResultArrayCallback<R>): void;
-    concat<T, R>(arr: Dictionary<T>, iterator: AsyncResultIterator<T, R[]>, callback?: AsyncResultArrayCallback<R>): void;
+    concat<T, R, E>(arr: T[], iterator: AsyncResultIterator<T, R[], E>, callback?: AsyncResultArrayCallback<R, E>): void;
+    concat<T, R, E>(arr: Dictionary<T>, iterator: AsyncResultIterator<T, R[], E>, callback?: AsyncResultArrayCallback<R, E>): void;
     concatSeries: typeof async.concat;
 
     // Control Flow
-    series<T>(tasks: AsyncFunction<T>[], callback?: AsyncResultArrayCallback<T>): void;
-    series<T>(tasks: Dictionary<AsyncFunction<T>>, callback?: AsyncResultObjectCallback<T>): void;
-    parallel<T>(tasks: Array<AsyncFunction<T>>, callback?: AsyncResultArrayCallback<T>): void;
-    parallel<T>(tasks: Dictionary<AsyncFunction<T>>, callback?: AsyncResultObjectCallback<T>): void;
-    parallelLimit<T>(tasks: Array<AsyncFunction<T>>, limit: number, callback?: AsyncResultArrayCallback<T>): void;
-    parallelLimit<T>(tasks: Dictionary<AsyncFunction<T>>, limit: number, callback?: AsyncResultObjectCallback<T>): void;
-    whilst(test: () => boolean, fn: AsyncVoidFunction, callback: ErrorCallback): void;
-    doWhilst(fn: AsyncVoidFunction, test: () => boolean, callback: ErrorCallback): void;
-    until(test: () => boolean, fn: AsyncVoidFunction, callback: ErrorCallback): void;
-    doUntil(fn: AsyncVoidFunction, test: () => boolean, callback: ErrorCallback): void;
-    during(test: (testCallback : AsyncBooleanResultCallback) => void, fn: AsyncVoidFunction, callback: ErrorCallback): void;
-    doDuring(fn: AsyncVoidFunction, test: (testCallback: AsyncBooleanResultCallback) => void, callback: ErrorCallback): void;
-    forever(next: (next : ErrorCallback) => void, errBack: ErrorCallback) : void;
-    waterfall<T>(tasks: Function[], callback?: AsyncResultCallback<T>): void;
+    series<T, E>(tasks: AsyncFunction<T, E>[], callback?: AsyncResultArrayCallback<T, E>): void;
+    series<T, E>(tasks: Dictionary<AsyncFunction<T, E>>, callback?: AsyncResultObjectCallback<T, E>): void;
+    parallel<T, E>(tasks: Array<AsyncFunction<T, E>>, callback?: AsyncResultArrayCallback<T, E>): void;
+    parallel<T, E>(tasks: Dictionary<AsyncFunction<T, E>>, callback?: AsyncResultObjectCallback<T, E>): void;
+    parallelLimit<T, E>(tasks: Array<AsyncFunction<T, E>>, limit: number, callback?: AsyncResultArrayCallback<T, E>): void;
+    parallelLimit<T, E>(tasks: Dictionary<AsyncFunction<T, E>>, limit: number, callback?: AsyncResultObjectCallback<T, E>): void;
+    whilst<E>(test: () => boolean, fn: AsyncVoidFunction<E>, callback: ErrorCallback<E>): void;
+    doWhilst<E>(fn: AsyncVoidFunction<E>, test: () => boolean, callback: ErrorCallback<E>): void;
+    until<E>(test: () => boolean, fn: AsyncVoidFunction<E>, callback: ErrorCallback<E>): void;
+    doUntil<E>(fn: AsyncVoidFunction<E>, test: () => boolean, callback: ErrorCallback<E>): void;
+    during<E>(test: (testCallback : AsyncBooleanResultCallback<E>) => void, fn: AsyncVoidFunction<E>, callback: ErrorCallback<E>): void;
+    doDuring<E>(fn: AsyncVoidFunction<E>, test: (testCallback: AsyncBooleanResultCallback<E>) => void, callback: ErrorCallback<E>): void;
+    forever<E>(next: (next : ErrorCallback<E>) => void, errBack: ErrorCallback<E>) : void;
+    waterfall<T, E>(tasks: Function[], callback?: AsyncResultCallback<T,E>): void;
     compose(...fns: Function[]): Function;
     seq(...fns: Function[]): Function;
     applyEach(fns: Function[], argsAndCallback: any[]): void;           // applyEach(fns, args..., callback). TS does not support ... for a middle argument. Callback is optional.
     applyEachSeries(fns: Function[], argsAndCallback: any[]): void;     // applyEachSeries(fns, args..., callback). TS does not support ... for a middle argument. Callback is optional.
-    queue<T>(worker: AsyncWorker<T>, concurrency?: number): AsyncQueue<T>;
-    priorityQueue<T>(worker: AsyncWorker<T>, concurrency: number): AsyncPriorityQueue<T>;
-    cargo(worker : (tasks: any[], callback : ErrorCallback) => void, payload? : number) : AsyncCargo;
-    auto(tasks: any, concurrency?: number, callback?: AsyncResultCallback<any>): void;
-    autoInject(tasks: any, callback?: AsyncResultCallback<any>): void;
-    retry<T>(opts: number, task: (callback : AsyncResultCallback<T>, results: any) => void, callback:  AsyncResultCallback<any>): void;
-    retry<T>(opts: { times: number, interval: number|((retryCount: number) => number) }, task: (callback: AsyncResultCallback<T>, results : any) => void, callback:  AsyncResultCallback<any>): void;
-    retryable<T>(opts: number | {times: number, interval: number}, task: AsyncFunction<T>): AsyncFunction<T>;
-    apply(fn: Function, ...arguments: any[]): AsyncFunction<any>;
+    queue<T, E>(worker: AsyncWorker<T, E>, concurrency?: number): AsyncQueue<T>;
+    priorityQueue<T, E>(worker: AsyncWorker<T, E>, concurrency: number): AsyncPriorityQueue<T>;
+    cargo<E>(worker : (tasks: any[], callback : ErrorCallback<E>) => void, payload? : number) : AsyncCargo;
+    auto<E>(tasks: any, concurrency?: number, callback?: AsyncResultCallback<any, E>): void;
+    autoInject<E>(tasks: any, callback?: AsyncResultCallback<any, E>): void;
+    retry<T, E>(opts: number, task: (callback : AsyncResultCallback<T, E>, results: any) => void, callback:  AsyncResultCallback<any, E>): void;
+    retry<T, E>(opts: { times: number, interval: number|((retryCount: number) => number) }, task: (callback: AsyncResultCallback<T, E>, results : any) => void, callback:  AsyncResultCallback<any, E>): void;
+    retryable<T, E>(opts: number | {times: number, interval: number}, task: AsyncFunction<T, E>): AsyncFunction<T, E>;
+    apply<E>(fn: Function, ...arguments: any[]): AsyncFunction<any,E>;
     nextTick(callback: Function, ...args: any[]): void;
     setImmediate: typeof async.nextTick;
 
-    reflect<T>(fn: AsyncFunction<T>) : (callback: (err: void, result: {error?: Error, value?: T}) => void) => void;
-    reflectAll<T>(tasks: AsyncFunction<T>[]): ((callback: (err: void, result: {error?: Error, value?: T}) => void) => void)[];
+    reflect<T, E>(fn: AsyncFunction<T, E>) : (callback: (err: void, result: {error?: Error, value?: T}) => void) => void;
+    reflectAll<T, E>(tasks: AsyncFunction<T, E>[]): ((callback: (err: void, result: {error?: Error, value?: T}) => void) => void)[];
 
-    timeout<T>(fn: AsyncFunction<T>, milliseconds: number, info: any): AsyncFunction<T>;
+    timeout<T, E>(fn: AsyncFunction<T, E>, milliseconds: number, info: any): AsyncFunction<T, E>;
 
-    times<T> (n: number, iterator: AsyncResultIterator<number, T>, callback: AsyncResultArrayCallback<T>): void;
-    timesSeries<T>(n: number, iterator: AsyncResultIterator<number, T>, callback: AsyncResultArrayCallback<T>): void;
-    timesLimit<T>(n: number, limit: number, iterator: AsyncResultIterator<number, T>, callback: AsyncResultArrayCallback<T>): void;
+    times<T, E> (n: number, iterator: AsyncResultIterator<number, T, E>, callback: AsyncResultArrayCallback<T, E>): void;
+    timesSeries<T, E>(n: number, iterator: AsyncResultIterator<number, T, E>, callback: AsyncResultArrayCallback<T, E>): void;
+    timesLimit<T, E>(n: number, limit: number, iterator: AsyncResultIterator<number, T, E>, callback: AsyncResultArrayCallback<T, E>): void;
 
-    transform<T, R>(arr: T[], iteratee: (acc: R[], item: T, key: string, callback: (error?: Error) => void) => void): void;
-    transform<T, R>(arr: T[], acc: R[], iteratee: (acc: R[], item: T, key: string, callback: (error?: Error) => void) => void): void;
-    transform<T, R>(arr: {[key: string] : T}, iteratee: (acc: {[key: string] : R}, item: T, key: string, callback: (error?: Error) => void) => void): void;
-    transform<T, R>(arr: {[key: string] : T}, acc: {[key: string] : R}, iteratee: (acc: {[key: string] : R}, item: T, key: string, callback: (error?: Error) => void) => void): void;
+    transform<T, R, E>(arr: T[], iteratee: (acc: R[], item: T, key: string, callback: (error?: E) => void) => void): void;
+    transform<T, R, E>(arr: T[], acc: R[], iteratee: (acc: R[], item: T, key: string, callback: (error?: E) => void) => void): void;
+    transform<T, R, E>(arr: {[key: string] : T}, iteratee: (acc: {[key: string] : R}, item: T, key: string, callback: (error?: E) => void) => void): void;
+    transform<T, R, E>(arr: {[key: string] : T}, acc: {[key: string] : R}, iteratee: (acc: {[key: string] : R}, item: T, key: string, callback: (error?: E) => void) => void): void;
 
-    race<T>(tasks: (AsyncFunction<T>)[], callback: AsyncResultCallback<T>) : void;
+    race<T, E>(tasks: (AsyncFunction<T, E>)[], callback: AsyncResultCallback<T, E>) : void;
 
     // Utils
     memoize(fn: Function, hasher?: Function): Function;