diff --git a/types/node/index.d.ts b/types/node/index.d.ts
index d6bc8695ef..9753d31cc6 100644
--- a/types/node/index.d.ts
+++ b/types/node/index.d.ts
@@ -6409,17 +6409,17 @@ declare module "util" {
 
     export function promisify<TCustom extends Function>(fn: CustomPromisify<TCustom>): TCustom;
     export function promisify<TResult>(fn: (callback: (err: Error | null, result: TResult) => void) => void): () => Promise<TResult>;
-    export function promisify(fn: (callback: (err: Error | null) => void) => void): () => Promise<void>;
+    export function promisify(fn: (callback: (err?: Error | null) => void) => void): () => Promise<void>;
     export function promisify<T1, TResult>(fn: (arg1: T1, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1) => Promise<TResult>;
-    export function promisify<T1>(fn: (arg1: T1, callback: (err: Error | null) => void) => void): (arg1: T1) => Promise<void>;
+    export function promisify<T1>(fn: (arg1: T1, callback: (err?: Error | null) => void) => void): (arg1: T1) => Promise<void>;
     export function promisify<T1, T2, TResult>(fn: (arg1: T1, arg2: T2, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2) => Promise<TResult>;
-    export function promisify<T1, T2>(fn: (arg1: T1, arg2: T2, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2) => Promise<void>;
+    export function promisify<T1, T2>(fn: (arg1: T1, arg2: T2, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2) => Promise<void>;
     export function promisify<T1, T2, T3, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<TResult>;
-    export function promisify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<void>;
+    export function promisify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<void>;
     export function promisify<T1, T2, T3, T4, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<TResult>;
-    export function promisify<T1, T2, T3, T4>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>;
+    export function promisify<T1, T2, T3, T4>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>;
     export function promisify<T1, T2, T3, T4, T5, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<TResult>;
-    export function promisify<T1, T2, T3, T4, T5>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>;
+    export function promisify<T1, T2, T3, T4, T5>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>;
     export function promisify(fn: Function): Function;
     export namespace promisify {
         const custom: symbol;
diff --git a/types/node/node-tests.ts b/types/node/node-tests.ts
index 266dc5d97e..5a87685a68 100644
--- a/types/node/node-tests.ts
+++ b/types/node/node-tests.ts
@@ -862,6 +862,7 @@ namespace util_tests {
         var arg0NoResult: () => Promise<any> = util.promisify((cb: (err: Error) => void): void => { });
         var arg1: (arg: string) => Promise<number> = util.promisify((arg: string, cb: (err: Error, result: number) => void): void => { });
         var arg1NoResult: (arg: string) => Promise<any> = util.promisify((arg: string, cb: (err: Error) => void): void => { });
+        var cbOptionalError: () => Promise<void> = util.promisify((cb: (err?: Error | null) => void): void => { cb(); });
         assert(typeof util.promisify.custom === 'symbol');
         // util.deprecate
         const foo = () => {};
diff --git a/types/node/v8/index.d.ts b/types/node/v8/index.d.ts
index dc44245c59..729a0c0da8 100644
--- a/types/node/v8/index.d.ts
+++ b/types/node/v8/index.d.ts
@@ -5688,17 +5688,17 @@ declare module "util" {
 
     export function promisify<TCustom extends Function>(fn: CustomPromisify<TCustom>): TCustom;
     export function promisify<TResult>(fn: (callback: (err: Error | null, result: TResult) => void) => void): () => Promise<TResult>;
-    export function promisify(fn: (callback: (err: Error | null) => void) => void): () => Promise<void>;
+    export function promisify(fn: (callback: (err?: Error | null) => void) => void): () => Promise<void>;
     export function promisify<T1, TResult>(fn: (arg1: T1, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1) => Promise<TResult>;
-    export function promisify<T1>(fn: (arg1: T1, callback: (err: Error | null) => void) => void): (arg1: T1) => Promise<void>;
+    export function promisify<T1>(fn: (arg1: T1, callback: (err?: Error | null) => void) => void): (arg1: T1) => Promise<void>;
     export function promisify<T1, T2, TResult>(fn: (arg1: T1, arg2: T2, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2) => Promise<TResult>;
-    export function promisify<T1, T2>(fn: (arg1: T1, arg2: T2, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2) => Promise<void>;
+    export function promisify<T1, T2>(fn: (arg1: T1, arg2: T2, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2) => Promise<void>;
     export function promisify<T1, T2, T3, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<TResult>;
-    export function promisify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<void>;
+    export function promisify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<void>;
     export function promisify<T1, T2, T3, T4, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<TResult>;
-    export function promisify<T1, T2, T3, T4>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>;
+    export function promisify<T1, T2, T3, T4>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>;
     export function promisify<T1, T2, T3, T4, T5, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<TResult>;
-    export function promisify<T1, T2, T3, T4, T5>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>;
+    export function promisify<T1, T2, T3, T4, T5>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>;
     export function promisify(fn: Function): Function;
     export namespace promisify {
         const custom: symbol;
diff --git a/types/node/v8/node-tests.ts b/types/node/v8/node-tests.ts
index d89e6faacc..e1d14b9089 100644
--- a/types/node/v8/node-tests.ts
+++ b/types/node/v8/node-tests.ts
@@ -819,6 +819,8 @@ namespace util_tests {
         var arg0NoResult: () => Promise<any> = util.promisify((cb: (err: Error) => void): void => { });
         var arg1: (arg: string) => Promise<number> = util.promisify((arg: string, cb: (err: Error, result: number) => void): void => { });
         var arg1NoResult: (arg: string) => Promise<any> = util.promisify((arg: string, cb: (err: Error) => void): void => { });
+        // The following test requires typescript >= 2.4, but definitions currently tested with typescript@2.1
+        // var cbOptionalError: () => Promise<void> = util.promisify((cb: (err?: Error | null) => void): void => { cb(); });
         assert(typeof util.promisify.custom === 'symbol');
         // util.deprecate
         const foo = () => {};
diff --git a/types/node/v9/index.d.ts b/types/node/v9/index.d.ts
index fd89e18e16..ba7347e849 100644
--- a/types/node/v9/index.d.ts
+++ b/types/node/v9/index.d.ts
@@ -5772,17 +5772,17 @@ declare module "util" {
 
     export function promisify<TCustom extends Function>(fn: CustomPromisify<TCustom>): TCustom;
     export function promisify<TResult>(fn: (callback: (err: Error | null, result: TResult) => void) => void): () => Promise<TResult>;
-    export function promisify(fn: (callback: (err: Error | null) => void) => void): () => Promise<void>;
+    export function promisify(fn: (callback: (err?: Error | null) => void) => void): () => Promise<void>;
     export function promisify<T1, TResult>(fn: (arg1: T1, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1) => Promise<TResult>;
-    export function promisify<T1>(fn: (arg1: T1, callback: (err: Error | null) => void) => void): (arg1: T1) => Promise<void>;
+    export function promisify<T1>(fn: (arg1: T1, callback: (err?: Error | null) => void) => void): (arg1: T1) => Promise<void>;
     export function promisify<T1, T2, TResult>(fn: (arg1: T1, arg2: T2, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2) => Promise<TResult>;
-    export function promisify<T1, T2>(fn: (arg1: T1, arg2: T2, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2) => Promise<void>;
+    export function promisify<T1, T2>(fn: (arg1: T1, arg2: T2, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2) => Promise<void>;
     export function promisify<T1, T2, T3, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<TResult>;
-    export function promisify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<void>;
+    export function promisify<T1, T2, T3>(fn: (arg1: T1, arg2: T2, arg3: T3, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3) => Promise<void>;
     export function promisify<T1, T2, T3, T4, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<TResult>;
-    export function promisify<T1, T2, T3, T4>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>;
+    export function promisify<T1, T2, T3, T4>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4) => Promise<void>;
     export function promisify<T1, T2, T3, T4, T5, TResult>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: Error | null, result: TResult) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<TResult>;
-    export function promisify<T1, T2, T3, T4, T5>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>;
+    export function promisify<T1, T2, T3, T4, T5>(fn: (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5, callback: (err?: Error | null) => void) => void): (arg1: T1, arg2: T2, arg3: T3, arg4: T4, arg5: T5) => Promise<void>;
     export function promisify(fn: Function): Function;
     export namespace promisify {
         const custom: symbol;
diff --git a/types/node/v9/node-tests.ts b/types/node/v9/node-tests.ts
index ace737fa3b..03f641e216 100644
--- a/types/node/v9/node-tests.ts
+++ b/types/node/v9/node-tests.ts
@@ -845,6 +845,7 @@ namespace util_tests {
         var arg0NoResult: () => Promise<any> = util.promisify((cb: (err: Error) => void): void => { });
         var arg1: (arg: string) => Promise<number> = util.promisify((arg: string, cb: (err: Error, result: number) => void): void => { });
         var arg1NoResult: (arg: string) => Promise<any> = util.promisify((arg: string, cb: (err: Error) => void): void => { });
+        var cbOptionalError: () => Promise<void> = util.promisify((cb: (err?: Error | null) => void): void => { cb(); });
         assert(typeof util.promisify.custom === 'symbol');
         // util.deprecate
         const foo = () => {};