diff --git a/sw.js b/sw.js
index 1494c6c..b781880 100644
--- a/sw.js
+++ b/sw.js
@@ -33,7 +33,7 @@ async function cacheFirst(request) {
       const csp = url.searchParams.get('csp')
       return new Response(html, {
         headers: {
-          'Content-Type': 'text/html',
+          'Content-Type': 'text/html; charset=utf-8',
           'Content-Security-Policy': csp,
         }
       })