diff --git a/addons/bus/static/tests/helpers/mock_websocket.js b/addons/bus/static/tests/helpers/mock_websocket.js
index ab5b04a2f1f..5fa2e7e66b9 100644
--- a/addons/bus/static/tests/helpers/mock_websocket.js
+++ b/addons/bus/static/tests/helpers/mock_websocket.js
@@ -73,7 +73,12 @@ export function patchWebsocketWorkerWithCleanup(params = {}) {
     websocketWorker = websocketWorker || new WebsocketWorker('wss://odoo.com/websocket');
     patchWithCleanup(browser, {
         SharedWorker: function () {
-            return new SharedWorkerMock(websocketWorker);
+            const sharedWorker = new SharedWorkerMock(websocketWorker);
+            registerCleanup(() => {
+                sharedWorker._messageChannel.port1.close();
+                sharedWorker._messageChannel.port2.close();
+            });
+            return sharedWorker;
         },
     }, { pure: true });
     registerCleanup(() => {
diff --git a/addons/web/static/src/owl2_compatibility/event_target.js b/addons/web/static/src/owl2_compatibility/event_target.js
index 8ef1c23ef29..868ea2a7e71 100644
--- a/addons/web/static/src/owl2_compatibility/event_target.js
+++ b/addons/web/static/src/owl2_compatibility/event_target.js
@@ -14,20 +14,29 @@
         }
         on(type, target, callback) {
             if (!this.targetsCallbacks.has(target)) {
-                this.targetsCallbacks.set(target, []);
+                this.targetsCallbacks.set(target, {});
             }
             callback = wrapCallback(target, callback);
-            this.targetsCallbacks.get(target).push(callback);
+            const listeners = this.targetsCallbacks.get(target);
+            if (!listeners[type]) {
+                listeners[type] = new Set();
+            }
+            listeners[type].add(callback);
             return this.addEventListener(type, callback);
         }
         off(type, target) {
-            const cbs = this.targetsCallbacks.get(target);
-            if (!cbs) {
+            const listeners = this.targetsCallbacks.get(target);
+            if (!listeners || !Object.hasOwnProperty.call(listeners, type)) {
                 return;
             }
+            const cbs = listeners[type];
             for (const callback of cbs) {
                 this.removeEventListener(type, callback);
             }
+            delete cbs[type];
+            if (Object.keys(cbs).length === 0) {
+                this.targetsCallbacks.delete(target);
+            }
         }
     };
 })();