diff --git a/packages/theme/src/cli/utilities/theme-environment/local-assets.ts b/packages/theme/src/cli/utilities/theme-environment/local-assets.ts
index 2c3f676fdc..d8cfc20107 100644
--- a/packages/theme/src/cli/utilities/theme-environment/local-assets.ts
+++ b/packages/theme/src/cli/utilities/theme-environment/local-assets.ts
@@ -130,7 +130,7 @@ function handleStylesCss(ctx: DevServerContext, event: H3Event) {
 
   return serveStatic(event, {
     getContents: () => stylesheet,
-    getMeta: () => ({type: 'text/css', size: stylesheet.length, mtime: new Date()}),
+    getMeta: () => ({type: 'text/css', size: Buffer.byteLength(stylesheet), mtime: new Date()}),
   })
 }
 
@@ -190,7 +190,7 @@ function handleBlockScriptsJs(ctx: DevServerContext, event: H3Event, kind: 'bloc
 
   return serveStatic(event, {
     getContents: () => javascript,
-    getMeta: () => ({type: 'text/javascript', size: javascript.length, mtime: new Date()}),
+    getMeta: () => ({type: 'text/javascript', size: Buffer.byteLength(javascript), mtime: new Date()}),
   })
 }