diff --git a/background/usercss-helper.js b/background/usercss-helper.js
index 8a9a3a0c..26bf92d8 100644
--- a/background/usercss-helper.js
+++ b/background/usercss-helper.js
@@ -27,24 +27,18 @@ var usercssHelper = (() => {
   }
 
   // Parse the source and find the duplication
-  // style: {sourceCode: string, checkDup: boolean}
-  function build(request, noReject) {
-    const pending = buildMeta(request)
-      .then(style => Promise.all([buildCode(style), checkDup(style)]))
+  function build({sourceCode, checkDup = false}, noReject) {
+    const pending = buildMeta({sourceCode})
+      .then(style => Promise.all([
+        buildCode(style),
+        checkDup && findDup(style)
+      ]))
       .then(([style, dup]) => ({style, dup}));
 
     if (noReject) {
       return wrapReject(pending);
     }
     return pending;
-
-    function checkDup(style) {
-      const {checkDup} = style;
-      delete style.checkDup;
-      if (checkDup) {
-        return findDup(style);
-      }
-    }
   }
 
   function save(style, noReject) {
diff --git a/content/install-user-css.js b/content/install-user-css.js
index 99c31496..8e4c61fc 100644
--- a/content/install-user-css.js
+++ b/content/install-user-css.js
@@ -1,14 +1,6 @@
+/* global runtimeSend */
 'use strict';
 
-function runtimeSend(request) {
-  return new Promise((resolve, reject) => {
-    chrome.runtime.sendMessage(
-      request,
-      ({status, result}) => (status === 'error' ? reject : resolve)(result)
-    );
-  });
-}
-
 function createSourceLoader() {
   let source;
 
diff --git a/content/util.js b/content/util.js
new file mode 100644
index 00000000..c639440f
--- /dev/null
+++ b/content/util.js
@@ -0,0 +1,10 @@
+'use strict';
+
+function runtimeSend(request) {
+  return new Promise((resolve, reject) => {
+    chrome.runtime.sendMessage(
+      request,
+      ({status, result}) => (status === 'error' ? reject : resolve)(result)
+    );
+  });
+}
diff --git a/install-usercss.html b/install-usercss.html
index b2f6b78a..aa7762e1 100644
--- a/install-usercss.html
+++ b/install-usercss.html
@@ -83,6 +83,7 @@
       </div>
     </div>
   </div>
+  <script src="/content/util.js"></script>
   <script src="/install-usercss/install-usercss.js"></script>
 </body>
 </html>
\ No newline at end of file
diff --git a/install-usercss/install-usercss.js b/install-usercss/install-usercss.js
index 7a2862fc..0a8846d4 100644
--- a/install-usercss/install-usercss.js
+++ b/install-usercss/install-usercss.js
@@ -1,4 +1,4 @@
-/* global CodeMirror semverCompare makeLink closeCurrentTab */
+/* global CodeMirror semverCompare makeLink closeCurrentTab runtimeSend */
 'use strict';
 
 (() => {
@@ -153,15 +153,6 @@
     main.insertBefore(buildWarning(err), main.firstChild);
   }
 
-  function runtimeSend(request) {
-    return new Promise((resolve, reject) => {
-      chrome.runtime.sendMessage(
-        request,
-        ({status, result}) => (status === 'error' ? reject : resolve)(result)
-      );
-    });
-  }
-
   function install(style) {
     const request = Object.assign(style, {
       method: 'saveUsercss',
diff --git a/manifest.json b/manifest.json
index ffc059b5..4d567ffb 100644
--- a/manifest.json
+++ b/manifest.json
@@ -59,7 +59,7 @@
       "include_globs": ["*.user.css", "*.user.styl"],
       "run_at": "document_idle",
       "all_frames": false,
-      "js": ["content/install-user-css.js"]
+      "js": ["content/util.js", "content/install-user-css.js"]
     }
   ],
   "browser_action": {