diff --git a/build-fallback-worker.js b/build-fallback-worker.js
index af3ce017..bdffc5fc 100644
--- a/build-fallback-worker.js
+++ b/build-fallback-worker.js
@@ -20,7 +20,7 @@ const getFallbackEnvs = ({fallbacks, basedir, id}) => {
 
     if (!pagesDir) return
 
-    const offlines = ['tsx', 'ts', 'jsx', 'js', 'mdx']
+    const offlines = pageExtensions
       .map(ext => path.join(pagesDir, `_offline.${ext}`))
       .filter(entry => fs.existsSync(entry))
     if (offlines.length === 1) {
@@ -54,8 +54,8 @@ const getFallbackEnvs = ({fallbacks, basedir, id}) => {
   return envs
 }
 
-const buildFallbackWorker = ({ id, fallbacks, basedir, destdir, success, minify }) => {
-  const envs = getFallbackEnvs({fallbacks, basedir, id})
+const buildFallbackWorker = ({ id, fallbacks, basedir, destdir, success, minify, pageExtensions }) => {
+  const envs = getFallbackEnvs({fallbacks, basedir, id, pageExtensions})
   if (!envs) return false
 
   const name = `fallback-${id}.js`
diff --git a/index.js b/index.js
index cc002cc6..8cb8849c 100644
--- a/index.js
+++ b/index.js
@@ -19,7 +19,7 @@ module.exports = (nextConfig = {}) => ({
       webpack,
       buildId,
       dev,
-      config: { distDir = '.next', pwa = {}, experimental = {}}
+      config: { distDir = '.next', pwa = {}, pageExtensions = ['tsx', 'ts', 'jsx', 'js', 'mdx'], experimental = {}}
     } = options
 
     let basePath = options.config.basePath
@@ -182,7 +182,8 @@ module.exports = (nextConfig = {}) => ({
               }
             })
           },
-          minify: !dev
+          minify: !dev,
+          pageExtensions
         })
       }