diff --git a/src/event-handler/index.ts b/src/event-handler/index.ts
index 24393e6e1..5695e4562 100644
--- a/src/event-handler/index.ts
+++ b/src/event-handler/index.ts
@@ -1,4 +1,4 @@
-import { createLogger } from "../createLogger";
+import { createLogger } from "../createLogger.js";
 import type {
   EmitterWebhookEvent,
   EmitterWebhookEventName,
@@ -11,9 +11,9 @@ import {
   receiverOn as on,
   receiverOnAny as onAny,
   receiverOnError as onError,
-} from "./on";
-import { receiverHandle as receive } from "./receive";
-import { removeListener } from "./remove-listener";
+} from "./on.js";
+import { receiverHandle as receive } from "./receive.js";
+import { removeListener } from "./remove-listener.js";
 
 interface EventHandler<TTransformed> {
   on<E extends EmitterWebhookEventName>(
diff --git a/src/event-handler/on.ts b/src/event-handler/on.ts
index 36f4c0b73..ab0e4c305 100644
--- a/src/event-handler/on.ts
+++ b/src/event-handler/on.ts
@@ -1,4 +1,4 @@
-import { emitterEventNames } from "../generated/webhook-names";
+import { emitterEventNames } from "../generated/webhook-names.js";
 import {
   EmitterWebhookEvent,
   EmitterWebhookEventName,
diff --git a/src/index.ts b/src/index.ts
index b8e1da5b8..3658b6c40 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,8 +1,8 @@
 import { sign, verify } from "@octokit/webhooks-methods";
 
-import { createLogger } from "./createLogger";
-import { createEventHandler } from "./event-handler/index";
-import { verifyAndReceive } from "./verify-and-receive";
+import { createLogger } from "./createLogger.js";
+import { createEventHandler } from "./event-handler/index.js";
+import { verifyAndReceive } from "./verify-and-receive.js";
 import {
   EmitterWebhookEvent,
   EmitterWebhookEventName,
@@ -13,7 +13,7 @@ import {
   WebhookEventHandlerError,
 } from "./types";
 
-export { createNodeMiddleware } from "./middleware/node/index";
+export { createNodeMiddleware } from "./middleware/node/index.js";
 
 // U holds the return value of `transform` function in Options
 class Webhooks<TTransformed = unknown> {
diff --git a/src/middleware/node/index.ts b/src/middleware/node/index.ts
index 06312ba3b..1b41da1f3 100644
--- a/src/middleware/node/index.ts
+++ b/src/middleware/node/index.ts
@@ -1,7 +1,7 @@
-import { createLogger } from "../../createLogger";
-import { Webhooks } from "../../index";
-import { middleware } from "./middleware";
-import { onUnhandledRequestDefault } from "./on-unhandled-request-default";
+import { createLogger } from "../../createLogger.js";
+import { Webhooks } from "../../index.js";
+import { middleware } from "./middleware.js";
+import { onUnhandledRequestDefault } from "./on-unhandled-request-default.js";
 import { MiddlewareOptions } from "./types";
 
 export function createNodeMiddleware(
diff --git a/src/middleware/node/types.ts b/src/middleware/node/types.ts
index 81c4e0ede..eaa608c56 100644
--- a/src/middleware/node/types.ts
+++ b/src/middleware/node/types.ts
@@ -4,7 +4,7 @@
 type IncomingMessage = any;
 type ServerResponse = any;
 
-import { Logger } from "../../createLogger";
+import { Logger } from "../../createLogger.js";
 
 export type MiddlewareOptions = {
   path?: string;
diff --git a/test/integration/event-handler-test.ts b/test/integration/event-handler-test.ts
index 8b5e15b15..5a706792d 100644
--- a/test/integration/event-handler-test.ts
+++ b/test/integration/event-handler-test.ts
@@ -1,6 +1,9 @@
-import { createEventHandler } from "../../src/event-handler";
+import { createEventHandler } from "../../src/event-handler/index.js";
 import { EmitterWebhookEvent, WebhookEventHandlerError } from "../../src/types";
-import { installationCreatedPayload, pushEventPayload } from "../fixtures";
+import {
+  installationCreatedPayload,
+  pushEventPayload,
+} from "../fixtures/index.js";
 
 test("events", async () => {
   const eventHandler = createEventHandler({});
diff --git a/test/integration/node-middleware.test.ts b/test/integration/node-middleware.test.ts
index aed49727d..31d940864 100644
--- a/test/integration/node-middleware.test.ts
+++ b/test/integration/node-middleware.test.ts
@@ -6,8 +6,8 @@ import { sign } from "@octokit/webhooks-methods";
 // import without types
 const express = require("express");
 
-import { Webhooks, createNodeMiddleware } from "../../src";
-import { pushEventPayload } from "../fixtures";
+import { Webhooks, createNodeMiddleware } from "../../src/index.js";
+import { pushEventPayload } from "../fixtures/index.js";
 
 let signatureSha256: string;
 
diff --git a/test/integration/smoke-test.ts b/test/integration/smoke-test.ts
index 1c53459a3..3cc72c171 100644
--- a/test/integration/smoke-test.ts
+++ b/test/integration/smoke-test.ts
@@ -1,4 +1,4 @@
-import { Webhooks, createEventHandler } from "../../src";
+import { Webhooks, createEventHandler } from "../../src/index.js";
 
 test("@octokit/webhooks", () => {
   const emitWarningSpy = jest.spyOn(process, "emitWarning");
diff --git a/test/integration/webhooks.test.ts b/test/integration/webhooks.test.ts
index 324776d4a..325ff1bca 100644
--- a/test/integration/webhooks.test.ts
+++ b/test/integration/webhooks.test.ts
@@ -1,4 +1,4 @@
-import { Webhooks, EmitterWebhookEvent } from "../../src";
+import { Webhooks, EmitterWebhookEvent } from "../../src/index.js";
 
 describe("Webhooks", () => {
   test("new Webhooks() without secret option", () => {
diff --git a/test/typescript-validate.ts b/test/typescript-validate.ts
index 055a80d5e..178104005 100644
--- a/test/typescript-validate.ts
+++ b/test/typescript-validate.ts
@@ -4,7 +4,7 @@ import {
   EmitterWebhookEvent,
   WebhookError,
   createNodeMiddleware,
-} from "../src/index";
+} from "../src/index.js";
 import { createServer } from "http";
 import { HandlerFunction, EmitterWebhookEventName } from "../src/types";
 
diff --git a/test/unit/createLogger-test.ts b/test/unit/createLogger-test.ts
index 568a6fded..1c1863022 100644
--- a/test/unit/createLogger-test.ts
+++ b/test/unit/createLogger-test.ts
@@ -1,4 +1,4 @@
-import { createLogger } from "../../src/createLogger";
+import { createLogger } from "../../src/createLogger.js";
 
 const noop = () => {};
 
diff --git a/test/unit/event-handler-on-test.ts b/test/unit/event-handler-on-test.ts
index 460b9c426..3c666e998 100644
--- a/test/unit/event-handler-on-test.ts
+++ b/test/unit/event-handler-on-test.ts
@@ -1,4 +1,4 @@
-import { receiverOn } from "../../src/event-handler/on";
+import { receiverOn } from "../../src/event-handler/on.js";
 import { State } from "../../src/types";
 
 function noop() {}
diff --git a/test/unit/event-handler-receive-test.ts b/test/unit/event-handler-receive-test.ts
index 240566eba..224c475c3 100644
--- a/test/unit/event-handler-receive-test.ts
+++ b/test/unit/event-handler-receive-test.ts
@@ -1,4 +1,4 @@
-import { receiverHandle as receive } from "../../src/event-handler/receive";
+import { receiverHandle as receive } from "../../src/event-handler/receive.js";
 import { State } from "../../src/types";
 
 const state: State = {
diff --git a/test/unit/event-handler-remove-listener-test.ts b/test/unit/event-handler-remove-listener-test.ts
index 231be6561..8fec9d945 100644
--- a/test/unit/event-handler-remove-listener-test.ts
+++ b/test/unit/event-handler-remove-listener-test.ts
@@ -1,4 +1,4 @@
-import { removeListener } from "../../src/event-handler/remove-listener";
+import { removeListener } from "../../src/event-handler/remove-listener.js";
 import { State } from "../../src/types";
 
 test("remove-listener: single listener", () => {
diff --git a/test/unit/event-handler-wrap-error-handler-test.ts b/test/unit/event-handler-wrap-error-handler-test.ts
index 157b60a65..50a1e9940 100644
--- a/test/unit/event-handler-wrap-error-handler-test.ts
+++ b/test/unit/event-handler-wrap-error-handler-test.ts
@@ -1,4 +1,4 @@
-import { wrapErrorHandler } from "../../src/event-handler/wrap-error-handler";
+import { wrapErrorHandler } from "../../src/event-handler/wrap-error-handler.js";
 
 const noop = () => {};