diff --git a/bottleneck.d.ts b/bottleneck.d.ts
index 0540b5c..e074b1b 100644
--- a/bottleneck.d.ts
+++ b/bottleneck.d.ts
@@ -491,7 +491,7 @@ declare module "bottleneck" {
         on(name: "queued",    fn: (info: Bottleneck.EventInfoQueued) => void): void;
         on(name: "scheduled", fn: (info: Bottleneck.EventInfo) => void): void;
         on(name: "executing", fn: (info: Bottleneck.EventInfoRetryable) => void): void;
-        on(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number | void> | number | void): void;
+        on(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number | void | null> | number | void | null): void;
         on(name: "retry",     fn: (message: string, info: Bottleneck.EventInfoRetryable) => void): void;
         on(name: "done",      fn: (info: Bottleneck.EventInfoRetryable) => void): void;
 
@@ -511,7 +511,7 @@ declare module "bottleneck" {
         once(name: "queued",    fn: (info: Bottleneck.EventInfoQueued) => void): void;
         once(name: "scheduled", fn: (info: Bottleneck.EventInfo) => void): void;
         once(name: "executing", fn: (info: Bottleneck.EventInfoRetryable) => void): void;
-        once(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number | void> | number | void): void;
+        once(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number | void | null> | number | void | null): void;
         once(name: "retry",     fn: (message: string, info: Bottleneck.EventInfoRetryable) => void): void;
         once(name: "done",      fn: (info: Bottleneck.EventInfoRetryable) => void): void;
 
diff --git a/bottleneck.d.ts.ejs b/bottleneck.d.ts.ejs
index 8af8de3..bb17c63 100644
--- a/bottleneck.d.ts.ejs
+++ b/bottleneck.d.ts.ejs
@@ -491,7 +491,7 @@ declare module "bottleneck" {
         on(name: "queued",    fn: (info: Bottleneck.EventInfoQueued) => void): void;
         on(name: "scheduled", fn: (info: Bottleneck.EventInfo) => void): void;
         on(name: "executing", fn: (info: Bottleneck.EventInfoRetryable) => void): void;
-        on(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number> | void): void;
+        on(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number | void | null> | number | void | null): void;
         on(name: "retry",     fn: (message: string, info: Bottleneck.EventInfoRetryable) => void): void;
         on(name: "done",      fn: (info: Bottleneck.EventInfoRetryable) => void): void;
 
@@ -511,7 +511,7 @@ declare module "bottleneck" {
         once(name: "queued",    fn: (info: Bottleneck.EventInfoQueued) => void): void;
         once(name: "scheduled", fn: (info: Bottleneck.EventInfo) => void): void;
         once(name: "executing", fn: (info: Bottleneck.EventInfoRetryable) => void): void;
-        once(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number> | void): void;
+        once(name: "failed",    fn: (error: any, info: Bottleneck.EventInfoRetryable) => Promise<number | void | null> | number | void | null): void;
         once(name: "retry",     fn: (message: string, info: Bottleneck.EventInfoRetryable) => void): void;
         once(name: "done",      fn: (info: Bottleneck.EventInfoRetryable) => void): void;
 
diff --git a/test.ts b/test.ts
index 4b348fa..bf064a7 100644
--- a/test.ts
+++ b/test.ts
@@ -119,6 +119,40 @@ limiter.on('failed', (error, info) => {
   return Promise.resolve(10)
 })
 
+limiter.on('failed', (error, info) => {
+  checkEventInfo(info)
+  const message: string = error.message;
+  const count: number = info.retryCount;
+  return Promise.resolve(null)
+})
+
+limiter.on('failed', (error, info) => {
+  checkEventInfo(info)
+  const message: string = error.message;
+  const count: number = info.retryCount;
+  return Promise.resolve()
+})
+
+limiter.on('failed', (error, info) => {
+  checkEventInfo(info)
+  const message: string = error.message;
+  const count: number = info.retryCount;
+  return 10
+})
+
+limiter.on('failed', (error, info) => {
+  checkEventInfo(info)
+  const message: string = error.message;
+  const count: number = info.retryCount;
+  return null
+})
+
+limiter.on('failed', (error, info) => {
+  checkEventInfo(info)
+  const message: string = error.message;
+  const count: number = info.retryCount;
+})
+
 limiter.on('retry', (message: string, info) => {
   checkEventInfo(info)
   const count: number = info.retryCount;