diff --git a/src/serviceWorker.ts b/src/serviceWorker.ts
index 14ef129c..366f4832 100644
--- a/src/serviceWorker.ts
+++ b/src/serviceWorker.ts
@@ -28,7 +28,7 @@ type Config = {
 export function register(config?: Config) {
   if (process.env.NODE_ENV === 'production' && 'serviceWorker' in navigator) {
     // The URL constructor is available in all browsers that support SW.
-    const publicUrl = new URL(process.env.PUBLIC_URL, window.location.href);
+    const publicUrl = new URL(process.env.PUBLIC_URL as string, window.location.href);
     if (publicUrl.origin !== window.location.origin) {
       // Our service worker won't work if PUBLIC_URL is on a different origin
       // from what our page is served on. This might happen if a CDN is used to