diff --git a/src/service-worker/sw.js b/src/service-worker/sw.js
index 49c035027..3a69f3cfd 100644
--- a/src/service-worker/sw.js
+++ b/src/service-worker/sw.js
@@ -2,48 +2,12 @@
 
 // Backup the native ReadableStream because OpenPGP.js might modify it on Firefox
 const NativeReadableStream = ReadableStream;
-importScripts('openpgp/openpgp.min.js');
 import {createReadableStreamWrapper} from '@mattiasbuelens/web-streams-adapter';
+importScripts('openpgp/openpgp.min.js');
 
-
-/**
- * Convert a native ReadableStream to polyfill ReadableStream if ReadableStream class is polyfill.
- *
- * @param readableStream Native ReadableStream
- * @returns {*}
- */
-function toPolyfillReadableIfNeed(readableStream) {
-  // If not polyfilled
-  if (NativeReadableStream === ReadableStream) {
-    return readableStream;
-  // If ReadableStream is polyfill
-  } else {
-    // (base: https://github.com/MattiasBuelens/web-streams-adapter/tree/d76e3789d67b1ab3c91699ecc0c42bde897d2298)
-    // NOTE: ReadableStream is polyfill ReadableStream in this condition
-    const toPolyfillReadable = createReadableStreamWrapper(ReadableStream);
-    // Convert a native ReadableStream to polyfill ReadableStream
-    return toPolyfillReadable(readableStream);
-  }
-}
-
-/**
- * Convert a polyfill ReadableStream to native ReadableStream if ReadableStream class is polyfill.
- *
- * @param readableStream Native ReadableStream or polyfill ReadableStream
- * @returns {*}
- */
-function toNativeReadableIfNeed(readableStream) {
-  // If not polyfilled
-  if (NativeReadableStream === ReadableStream) {
-    return readableStream;
-    // If ReadableStream is polyfill
-  } else {
-    // (base: https://github.com/MattiasBuelens/web-streams-adapter/tree/d76e3789d67b1ab3c91699ecc0c42bde897d2298)
-    const toNativeReadable = createReadableStreamWrapper(NativeReadableStream);
-    // Convert a polyfill ReadableStream to native ReadableStream
-    return toNativeReadable(readableStream);
-  }
-}
+// Create convert functions
+const toPolyfillReadable = createReadableStreamWrapper(ReadableStream);
+const toNativeReadable = createReadableStreamWrapper(NativeReadableStream);
 
 // Generate random string with specific length
 function generateRandomString(len){
@@ -189,7 +153,7 @@ self.addEventListener('fetch', (event) => {
           openpgp.config.allow_unauthenticated_stream = true;
           // Decrypt the response body
           const decrypted = await openpgp.decrypt({
-            message: await openpgp.message.read(toPolyfillReadableIfNeed(res.body)),
+            message: await openpgp.message.read(toPolyfillReadable(res.body)),
             passwords: [password],
             format: 'binary'
           });
@@ -203,7 +167,7 @@ self.addEventListener('fetch', (event) => {
         }
       }
 
-      const downloadableRes = new Response(toNativeReadableIfNeed(plainStream), {
+      const downloadableRes = new Response(toNativeReadable(plainStream), {
         headers
       });
       return downloadableRes;