diff --git a/lib/middleware/karma.js b/lib/middleware/karma.js
index 32f6660d9..7b14463be 100644
--- a/lib/middleware/karma.js
+++ b/lib/middleware/karma.js
@@ -12,7 +12,6 @@
  */
 
 const path = require('path')
-const util = require('util')
 const url = require('url')
 const _ = require('lodash')
 
@@ -28,10 +27,6 @@ function urlparse (urlStr) {
 const common = require('./common')
 
 const VERSION = require('../constants').VERSION
-const SCRIPT_TAG = '<script type="%s" src="%s" %s></script>'
-const CROSSORIGIN_ATTRIBUTE = 'crossorigin="anonymous"'
-const LINK_TAG_CSS = '<link type="text/css" href="%s" rel="stylesheet">'
-const LINK_TAG_HTML = '<link href="%s" rel="import">'
 const SCRIPT_TYPE = {
   'js': 'text/javascript',
   'dart': 'application/dart',
@@ -202,12 +197,12 @@ function createKarmaMiddleware (
             scriptUrls.push(filePath)
 
             if (fileType === 'css' || (!fileType && fileExt === '.css')) {
-              scriptTags.push(util.format(LINK_TAG_CSS, filePath))
+              scriptTags.push(`<link type="text/css" href="${filePath}" rel="stylesheet">`)
               continue
             }
 
             if (fileType === 'html' || (!fileType && fileExt === '.html')) {
-              scriptTags.push(util.format(LINK_TAG_HTML, filePath))
+              scriptTags.push(`<link href="${filePath}" rel="import">`)
               continue
             }
 
@@ -215,8 +210,8 @@ function createKarmaMiddleware (
             const scriptFileType = (fileType || fileExt.substring(1))
             const scriptType = (SCRIPT_TYPE[scriptFileType] || 'text/javascript')
 
-            const crossOriginAttribute = includeCrossOriginAttribute ? CROSSORIGIN_ATTRIBUTE : ''
-            scriptTags.push(util.format(SCRIPT_TAG, scriptType, filePath, crossOriginAttribute))
+            const crossOriginAttribute = includeCrossOriginAttribute ? 'crossorigin="anonymous"' : ''
+            scriptTags.push(`<script type="${scriptType}" src="${filePath}" ${crossOriginAttribute}></script>`)
           }
 
           // TODO(vojta): don't compute if it's not in the template
@@ -227,7 +222,7 @@ function createKarmaMiddleware (
             // double quotes should not be allowed!
             filePath = filePath.replace(/'/g, '\\\'')
 
-            return util.format("  '%s': '%s'", filePath, file.sha)
+            return `  '${filePath}': '${file.sha}'`
           })
 
           const clientConfig = 'window.__karma__.config = ' + JSON.stringify(client) + ';\n'