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..907b922ea8 100644
--- a/packages/theme/src/cli/utilities/theme-environment/local-assets.ts
+++ b/packages/theme/src/cli/utilities/theme-environment/local-assets.ts
@@ -2,6 +2,7 @@ import {injectCdnProxy} from './proxy.js'
 import {parseServerEvent} from './server-utils.js'
 import {getLiquidTagContent} from './liquid-tag-content.js'
 import {lookupMimeType} from '@shopify/cli-kit/node/mimes'
+import {Buffer} from 'node:buffer'
 import {defineEventHandler, H3Event, serveStatic, setResponseHeader, sendError, createError} from 'h3'
 import {joinPath} from '@shopify/cli-kit/node/path'
 import type {Theme, ThemeAsset, VirtualFileSystem} from '@shopify/cli-kit/node/themes/types'
@@ -130,7 +131,7 @@ 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 +191,7 @@ 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()}),
   })
 }