diff --git a/platform/chromium/vapi-client.js b/platform/chromium/vapi-client.js
index 057687f51..e4099a20f 100644
--- a/platform/chromium/vapi-client.js
+++ b/platform/chromium/vapi-client.js
@@ -33,16 +33,16 @@
 
 self.vAPI = self.vAPI || {};
 
-// https://github.com/gorhill/uBlock/issues/456
-// Already injected?
-if ( vAPI.vapiClient ) {
-    return;
-}
-vAPI.vapiClient = true;
-
 var chrome = self.chrome;
 var vAPI = self.vAPI;
 
+// https://github.com/gorhill/uBlock/issues/456
+// Already injected?
+if ( vAPI.vapiClientInjected ) {
+    return;
+}
+vAPI.vapiClientInjected = true;
+
 vAPI.chrome = true;
 
 /******************************************************************************/
diff --git a/src/js/contentscript-end.js b/src/js/contentscript-end.js
index 13bbb3e77..6d229130d 100644
--- a/src/js/contentscript-end.js
+++ b/src/js/contentscript-end.js
@@ -21,12 +21,14 @@
 
 /* global vAPI */
 
-'use strict';
-
 /******************************************************************************/
 
 // Injected into content pages
 
+(function() {
+
+'use strict';
+
 /******************************************************************************/
 
 if ( vAPI.canExecuteContentScript() !== true ) {
@@ -35,10 +37,10 @@ if ( vAPI.canExecuteContentScript() !== true ) {
 
 // https://github.com/gorhill/uBlock/issues/456
 // Already injected?
-if ( vAPI.contentscriptEnd ) {
+if ( vAPI.contentscriptEndInjected ) {
     return;
 }
-vAPI.contentscriptEnd = true;
+vAPI.contentscriptEndInjected = true;
 
 /******************************************************************************/
 
@@ -684,3 +686,8 @@ var messager = vAPI.messaging.channel('contentscript-end.js');
 })();
 
 /******************************************************************************/
+/******************************************************************************/
+
+})();
+
+/******************************************************************************/
diff --git a/src/js/contentscript-start.js b/src/js/contentscript-start.js
index edc226369..2432562c2 100644
--- a/src/js/contentscript-start.js
+++ b/src/js/contentscript-start.js
@@ -46,10 +46,10 @@ if ( vAPI.canExecuteContentScript() !== true ) {
 
 // https://github.com/gorhill/uBlock/issues/456
 // Already injected?
-if ( vAPI.contentscriptStart ) {
+if ( vAPI.contentscriptStartInjected ) {
     return;
 }
-vAPI.contentscriptStart = true;
+vAPI.contentscriptStartInjected = true;
 
 /******************************************************************************/
 
@@ -64,7 +64,7 @@ var localMessager = vAPI.messaging.channel('contentscript-start.js');
 var cosmeticFilters = function(details) {
     var donthideCosmeticFilters = {};
     var hideCosmeticFilters = {};
-    style = document.createElement('style');
+    var style = document.createElement('style');
     style.setAttribute('id', 'ublock-preload-1ae7a5f130fc79b4fdb8a4272d9426b5');
     var donthide = details.cosmeticDonthide;
     var hide = details.cosmeticHide;