diff --git a/src/js/background.js b/src/js/background.js
index 87143a7ff..c3b074592 100644
--- a/src/js/background.js
+++ b/src/js/background.js
@@ -165,6 +165,10 @@ const µBlock = (( ) => { // jshint ignore:line
         selectedFilterLists: [],
         availableFilterLists: {},
 
+        // https://github.com/uBlockOrigin/uBlock-issues/issues/974
+        //   This can be used to defer filtering decision-making.
+        readyToFilter: false,
+
         pageStores: new Map(),
         pageStoresToken: 0,
 
diff --git a/src/js/messaging.js b/src/js/messaging.js
index 9cda182ea..b57b482fc 100644
--- a/src/js/messaging.js
+++ b/src/js/messaging.js
@@ -509,6 +509,7 @@ vAPI.messaging.listen({
 const µb = µBlock;
 
 const retrieveContentScriptParameters = function(senderDetails, request) {
+    if ( µb.readyToFilter !== true ) { return; }
     const { url, tabId, frameId } = senderDetails;
     if ( url === undefined || tabId === undefined || frameId === undefined ) {
         return;
diff --git a/src/js/scriptlets/should-inject-contentscript.js b/src/js/scriptlets/should-inject-contentscript.js
index 2e8440f34..b7458ad04 100644
--- a/src/js/scriptlets/should-inject-contentscript.js
+++ b/src/js/scriptlets/should-inject-contentscript.js
@@ -27,7 +27,7 @@
 // https://github.com/uBlockOrigin/uBlock-issues/issues/403
 //   If the content script was not boostrapped, give it another try.
 
-(function() {
+(( ) => {
     try {
         let status = vAPI.uBO !== true;
         if ( status === false && vAPI.bootstrap ) {
diff --git a/src/js/start.js b/src/js/start.js
index 826b74338..82f52a047 100644
--- a/src/js/start.js
+++ b/src/js/start.js
@@ -333,6 +333,10 @@ if ( selfieIsValid !== true ) {
 
 // Final initialization steps after all needed assets are in memory.
 
+// https://github.com/uBlockOrigin/uBlock-issues/issues/974
+//   This can be used to defer filtering decision-making.
+µb.readyToFilter = true;
+
 // Start network observers.
 µb.webRequest.start();