diff --git a/README.md b/README.md
index 0b5f0a8..962cb5d 100644
--- a/README.md
+++ b/README.md
@@ -96,9 +96,9 @@ module.exports = createConfig({
   plugins: [],
 
   /**
-   * entry file for umd/iife build
+   * entry file for umd/iife build, index here matches any of the extensions
    */
-  entryFile: 'index.js',
+  entryFile: 'index',
 
   /**
    * package export name for umd/iife,
diff --git a/src/config.ts b/src/config.ts
index 558bd86..8659339 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -9,7 +9,7 @@ export const config: Config = {
 
   plugins: [],
 
-  entryFile: 'index.js',
+  entryFile: 'index',
 
   moduleName: '',