diff --git a/apps/plugin-browser/src/pages/popup/popup-contents/action-center/one-off/infer-entities-action.tsx b/apps/plugin-browser/src/pages/popup/popup-contents/action-center/one-off/infer-entities-action.tsx
index dfdeccdfff4..21665f029ea 100644
--- a/apps/plugin-browser/src/pages/popup/popup-contents/action-center/one-off/infer-entities-action.tsx
+++ b/apps/plugin-browser/src/pages/popup/popup-contents/action-center/one-off/infer-entities-action.tsx
@@ -62,10 +62,10 @@ export const InferEntitiesAction = ({
     };
 
     try {
-      const sourceWebPage = await (browser.tabs.sendMessage(
-        activeTab.id,
-        message,
-      ) as Promise<GetTabContentReturn>);
+      const sourceWebPage = await browser.tabs.sendMessage<
+        GetTabContentRequest,
+        GetTabContentReturn
+      >(activeTab.id, message);
 
       void sendMessageToBackground({
         createAs,
diff --git a/apps/plugin-browser/src/scripts/background.ts b/apps/plugin-browser/src/scripts/background.ts
index 6dd14195db0..fc7adda01ce 100644
--- a/apps/plugin-browser/src/scripts/background.ts
+++ b/apps/plugin-browser/src/scripts/background.ts
@@ -5,8 +5,8 @@ import { getUser } from "../shared/get-user";
 import type {
   GetTabContentRequest,
   GetTabContentReturn,
-  Message,
 } from "../shared/messages";
+import { isWellFormattedMessage } from "../shared/messages";
 import {
   clearLocalStorage,
   getFromLocalStorage,
@@ -36,7 +36,11 @@ browser.runtime.onInstalled.addListener(({ reason }) => {
   }
 });
 
-browser.runtime.onMessage.addListener(async (message: Message, sender) => {
+browser.runtime.onMessage.addListener(async (message, sender) => {
+  if (!isWellFormattedMessage(message)) {
+    return `Unrecognised message format ${String(message)}`;
+  }
+
   if (sender.tab) {
     // We are not expecting any messages from the content script
     return;
@@ -63,9 +67,12 @@ browser.tabs.onUpdated.addListener((tabId, changeInfo) => {
             setTimeout(resolve, 2_000);
           });
 
-          const webPage = await (browser.tabs.sendMessage(tabId, {
+          const webPage = await browser.tabs.sendMessage<
+            GetTabContentRequest,
+            GetTabContentReturn
+          >(tabId, {
             type: "get-tab-content",
-          } satisfies GetTabContentRequest) as Promise<GetTabContentReturn>);
+          });
 
           const applicableRules = automaticInferenceConfig.rules.filter(
             ({ restrictToDomains }) => {
diff --git a/apps/plugin-browser/src/scripts/background/infer-entities/get-website-content.ts b/apps/plugin-browser/src/scripts/background/infer-entities/get-website-content.ts
index 331e9bbf5f4..56b7aa8ca2b 100644
--- a/apps/plugin-browser/src/scripts/background/infer-entities/get-website-content.ts
+++ b/apps/plugin-browser/src/scripts/background/infer-entities/get-website-content.ts
@@ -45,9 +45,12 @@ export const getWebsiteContent = async (urls: string[]) => {
       browser.tabs.onUpdated.addListener(tabChangeListener);
     });
 
-    const webPage = await (browser.tabs.sendMessage(tab.id, {
+    const webPage = await browser.tabs.sendMessage<
+      GetTabContentRequest,
+      GetTabContentReturn
+    >(tab.id, {
       type: "get-tab-content",
-    } satisfies GetTabContentRequest) as Promise<GetTabContentReturn>);
+    });
 
     webPages.push(webPage);
 
diff --git a/apps/plugin-browser/src/scripts/content.ts b/apps/plugin-browser/src/scripts/content.ts
index 19fe32bb204..50679f092b6 100644
--- a/apps/plugin-browser/src/scripts/content.ts
+++ b/apps/plugin-browser/src/scripts/content.ts
@@ -1,6 +1,12 @@
 import browser from "webextension-polyfill";
 
+import {
+  type GetTabContentReturn,
+  isWellFormattedMessage,
+} from "../shared/messages";
+
 /**
+ * @file
  * Content scripts operate in the context of the webpage itself, for reading and manipulating context.
  *
  * They have access to a limited set of browser APIs
@@ -10,11 +16,15 @@ import browser from "webextension-polyfill";
  *
  * You must update the extension if you amend this file, from the extensions manager page in the browser.
  */
-import type { GetTabContentReturn, Message } from "../shared/messages";
 
-// Promise based API (see: https://github.com/mozilla/webextension-polyfill/?tab=readme-ov-file#using-the-promise-based-apis)
+// Promise based API (see:
+// https://github.com/mozilla/webextension-polyfill/?tab=readme-ov-file#using-the-promise-based-apis)
 // eslint-disable-next-line @typescript-eslint/require-await
-browser.runtime.onMessage.addListener(async (message: Message, _sender) => {
+browser.runtime.onMessage.addListener(async (message) => {
+  if (!isWellFormattedMessage(message)) {
+    return `Unrecognised message format ${String(message)}`;
+  }
+
   if (message.type === "get-tab-content") {
     const docContent =
       document.querySelector("main") ?? document.querySelector("body");
diff --git a/apps/plugin-browser/src/shared/messages.ts b/apps/plugin-browser/src/shared/messages.ts
index acb8d5c1e24..ab3adeec31a 100644
--- a/apps/plugin-browser/src/shared/messages.ts
+++ b/apps/plugin-browser/src/shared/messages.ts
@@ -27,3 +27,8 @@ export type Message =
   | InferEntitiesRequest
   | CancelInferEntitiesRequest
   | GetTabContentRequest;
+
+export const isWellFormattedMessage = (message: unknown): message is Message =>
+  typeof message === "object" &&
+  message !== null &&
+  typeof (message as { type: unknown }).type === "string";