diff --git a/packages/core/index.d.ts b/packages/core/index.d.ts
index 92ce2c709..cf0a0c78b 100644
--- a/packages/core/index.d.ts
+++ b/packages/core/index.d.ts
@@ -96,12 +96,11 @@ export interface MiddyfiedHandler<
   before: AttachMiddlewareFn<TEvent, TResult, TErr, TContext, TInternal>
   after: AttachMiddlewareFn<TEvent, TResult, TErr, TContext, TInternal>
   onError: AttachMiddlewareFn<TEvent, TResult, TErr, TContext, TInternal>
-  handler: <TInputHandlerEventProps, TInputHandlerResultProps>(
+  handler: <TInputHandlerEventProps = TEvent, TInputHandlerResultProps = TResult>(
     handler: MiddlewareHandler<
     LambdaHandler<TInputHandlerEventProps, TInputHandlerResultProps>,
     TContext
     >
-    | LambdaHandler<TInputHandlerEventProps, TInputHandlerResultProps>
   ) => MiddyfiedHandler<TInputHandlerEventProps, TInputHandlerResultProps, TErr, TContext, TInternal>
 }
 
diff --git a/packages/core/index.test-d.ts b/packages/core/index.test-d.ts
index db39db2a7..bec0f5c09 100644
--- a/packages/core/index.test-d.ts
+++ b/packages/core/index.test-d.ts
@@ -5,7 +5,6 @@ import {
   APIGatewayProxyResult,
   Context,
   Handler as AWSLambdaHandler,
-  S3Handler,
   S3Event
 } from 'aws-lambda'
 
@@ -404,7 +403,7 @@ const handler1176 = middy(baseHandler)
 expectType<MiddyfiedHandler<any, any, Error, Context, {}>>(handler1176)
 
 // Issue #1182
-const s3Handler: S3Handler = async (event) => {
+const s3Handler = async (event: S3Event): Promise<void> => {
   await Promise.all(event.Records.map(async () => await Promise.resolve()))
 }