diff --git a/.presetterrc.json b/.presetterrc.json
index 9857885..1dc1e4b 100644
--- a/.presetterrc.json
+++ b/.presetterrc.json
@@ -5,7 +5,6 @@
     "config": {
         "tsconfig": {
             "compilerOptions": {
-                "allowImportingTsExtensions": true,
                 "module": "nodenext"
             }
         }
diff --git a/src/client.ts b/src/client.ts
index 6e89b42..514eede 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -14,9 +14,9 @@ import {
   uploadSmallFileRequest,
   uploadLargeFileRequest,
 } from "./upload.ts";
-import { downloadFile, getCidUrl, getMetadata } from "./download.ts";
+import { downloadFile, getCidUrl, getMetadata } from "./download.js";
 
-import { defaultPortalUrl, ensureUrl } from "./utils/url.ts";
+import { defaultPortalUrl, ensureUrl } from "./utils/url.js";
 
 import {
   buildRequestHeaders,
diff --git a/src/download.ts b/src/download.ts
index 2d477cb..eb8b17e 100644
--- a/src/download.ts
+++ b/src/download.ts
@@ -1,7 +1,7 @@
 import { ResponseType } from "axios";
 
-import { S5Client } from "./client.ts";
-import { BaseCustomOptions, DEFAULT_BASE_OPTIONS } from "./utils/options.ts";
+import { S5Client } from "./client.js";
+import { BaseCustomOptions, DEFAULT_BASE_OPTIONS } from "./utils/options.js";
 import path from "path";
 
 /**
diff --git a/src/index.ts b/src/index.ts
index f98cbef..329b04d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1 @@
-export { S5Client } from "./client.ts";
+export { S5Client } from "./client.js";
diff --git a/src/request.ts b/src/request.ts
index 58582a5..cccd790 100644
--- a/src/request.ts
+++ b/src/request.ts
@@ -1,12 +1,12 @@
 import { AxiosError, AxiosResponse, InternalAxiosRequestConfig } from "axios";
 
-import { S5Client } from "./client.ts";
+import { S5Client } from "./client.js";
 import {
   addUrlQuery,
   addUrlSubdomain,
   ensureUrlPrefix,
   makeUrl,
-} from "./utils/url.ts";
+} from "./utils/url.js";
 
 export type Headers = { [key: string]: string };
 
diff --git a/src/upload.ts b/src/upload.ts
index 576d82b..9bcfbee 100644
--- a/src/upload.ts
+++ b/src/upload.ts
@@ -4,11 +4,11 @@ import { DetailedError, HttpRequest, Upload } from "tus-js-client";
 import { blake3 } from "@noble/hashes/blake3";
 import { Buffer } from "buffer";
 
-import { getFileMimeType } from "./utils/file.ts";
-import { BaseCustomOptions, DEFAULT_BASE_OPTIONS } from "./utils/options.ts";
-import { S5Client } from "./client.ts";
-import type { JsonData } from "./utils/types.ts";
-import { buildRequestHeaders, buildRequestUrl } from "./request.ts";
+import { getFileMimeType } from "./utils/file.js";
+import { BaseCustomOptions, DEFAULT_BASE_OPTIONS } from "./utils/options.js";
+import { S5Client } from "./client.js";
+import type { JsonData } from "./utils/types.js";
+import { buildRequestHeaders, buildRequestUrl } from "./request.js";
 import { CID_HASH_TYPES, CID_TYPES } from "@lumeweb/libs5";
 
 /**