diff --git a/api/messaging/src/index.ts b/api/messaging/src/index.ts
index 8bbefadfa..44ee33776 100644
--- a/api/messaging/src/index.ts
+++ b/api/messaging/src/index.ts
@@ -12,18 +12,19 @@ export type {
 } from "./types"
 
 /**
- * Should only be called from CS or Ext Pages
- * Extension Id is required to send a message from a CS in the main world
- * TODO: Add a framework runtime check, using a global variable
+ * Send to Background Service Workers from Content Scripts or Extension pages.
+ * `extensionId` is required to send a message from a Content Script in the main world
  */
+// TODO: Add a framework runtime check, using a global variable
 export const sendToBackground: PlasmoMessaging.SendFx<MessageName> = async (
   req
 ) => {
-    return getExtRuntime().sendMessage(req.extensionId ?? null, req)
+  return getExtRuntime().sendMessage(req.extensionId ?? null, req)
 }
 
 /**
- * Send to CS from Ext pages or BGSW, default to active tab if no tabId is provided in the request
+ * Send to Content Scripts from Extension pages or Background Service Workers.
+ * Default to active tab if no tabId is provided in the request
  */
 export const sendToContentScript: PlasmoMessaging.SendFx = async (req) => {
   const tabId =
diff --git a/api/messaging/src/message.ts b/api/messaging/src/message.ts
index 1bc0dfdda..c4d282eb5 100644
--- a/api/messaging/src/message.ts
+++ b/api/messaging/src/message.ts
@@ -4,7 +4,11 @@ import { getExtRuntime } from "./utils"
 export const listen = <RequestBody, ResponseBody>(
   handler: PlasmoMessaging.Handler<string, RequestBody, ResponseBody>
 ) => {
-  const metaListener = async (req, sender, sendResponse) => {
+  const metaListener = async (
+    req: any,
+    sender: chrome.runtime.MessageSender,
+    sendResponse: (response?: ResponseBody) => void
+  ) => {
     await handler?.(
       {
         ...req,
@@ -16,9 +20,13 @@ export const listen = <RequestBody, ResponseBody>(
     )
   }
 
-  const listener = (req, sender, sendResponse) => {
+  const listener = (
+    req: any,
+    sender: chrome.runtime.MessageSender,
+    sendResponse: (response?: ResponseBody) => void
+  ) => {
     metaListener(req, sender, sendResponse)
-    return // Syncronous return to indicate this is an async listener
+    return true // Synchronous return to indicate this is an async listener
   }
 
   getExtRuntime().onMessage.addListener(listener)