diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6696631..ce3f086 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed `Warning: Accessing non-existent property 'MongoError' of module exports inside circular dependency` by downgrade to `mongodb@3.6.3`
 - Revert update session when touch (#351)
 - Fix cannot read property `lastModified` of null
+- Fix TS typing error
 
 ## [4.1.0] - 2021-02-22
 
diff --git a/src/lib/MongoStore.ts b/src/lib/MongoStore.ts
index 632024d..79a70dd 100644
--- a/src/lib/MongoStore.ts
+++ b/src/lib/MongoStore.ts
@@ -61,7 +61,7 @@ type ConcretConnectMongoOptions = {
   crypto: ConcretCryptoOptions
 }
 
-type ErrorOrNull = Error | null
+// type ErrorOrNull = Error | null
 
 type InternalSessionType = {
   _id: string
@@ -216,7 +216,7 @@ export default class MongoStore extends session.Store {
    */
   get(
     sid: string,
-    callback: (err: ErrorOrNull, session?: session.SessionData | null) => void
+    callback: (err: any, session?: session.SessionData | null) => void
   ): void {
     ;(async () => {
       try {
@@ -267,7 +267,7 @@ export default class MongoStore extends session.Store {
   set(
     sid: string,
     session: session.SessionData,
-    callback: (err: ErrorOrNull) => void = noop
+    callback: (err: any) => void = noop
   ): void {
     ;(async () => {
       try {
@@ -338,7 +338,7 @@ export default class MongoStore extends session.Store {
   touch(
     sid: string,
     session: session.SessionData & { lastModified?: Date },
-    callback: (err: ErrorOrNull) => void = noop
+    callback: (err: any) => void = noop
   ): void {
     ;(async () => {
       try {
@@ -394,7 +394,7 @@ export default class MongoStore extends session.Store {
    */
   all(
     callback: (
-      err: ErrorOrNull,
+      err: any,
       obj?:
         | session.SessionData[]
         | { [sid: string]: session.SessionData }
@@ -435,7 +435,7 @@ export default class MongoStore extends session.Store {
    * Destroy/delete a session from the store given a session ID (sid)
    * @param sid session ID
    */
-  destroy(sid: string, callback: (err: ErrorOrNull) => void = noop): void {
+  destroy(sid: string, callback: (err: any) => void = noop): void {
     debug(`MongoStore#destroy=${sid}`)
     this.collectionP
       .then((colleciton) =>
@@ -454,7 +454,7 @@ export default class MongoStore extends session.Store {
   /**
    * Get the count of all sessions in the store
    */
-  length(callback: (err: ErrorOrNull, length: number) => void): void {
+  length(callback: (err: any, length: number) => void): void {
     debug('MongoStore#length()')
     this.collectionP
       .then((collection) => collection.countDocuments())
@@ -466,7 +466,7 @@ export default class MongoStore extends session.Store {
   /**
    * Delete all sessions from the store.
    */
-  clear(callback: (err: ErrorOrNull) => void = noop): void {
+  clear(callback: (err: any) => void = noop): void {
     debug('MongoStore#clear()')
     this.collectionP
       .then((collection) => collection.drop())
diff --git a/src/test/integration.spec.ts b/src/test/integration.spec.ts
index c088c6e..4d05e3b 100644
--- a/src/test/integration.spec.ts
+++ b/src/test/integration.spec.ts
@@ -7,7 +7,7 @@ import { ConnectMongoOptions } from '../lib/MongoStore'
 
 declare module 'express-session' {
   interface SessionData {
-    views: number
+    [key: string]: any
   }
 }