diff --git a/types/chromecast-caf-receiver/cast.framework.d.ts b/types/chromecast-caf-receiver/cast.framework.d.ts
index f30ce78169..923c1c36b5 100644
--- a/types/chromecast-caf-receiver/cast.framework.d.ts
+++ b/types/chromecast-caf-receiver/cast.framework.d.ts
@@ -1204,9 +1204,9 @@ export class CastReceiverContext {
     removeEventListener(type: system.EventType, handler: EventHandler): void;
 
     /**
-     * Sends a message to a specific sender.
+     * Sends a message to a specific sender or broadcasts it to all connected senders (to broadcast pass undefined as a senderId).
      */
-    sendCustomMessage(namespace: string, senderId: string, message: any): void;
+    sendCustomMessage(namespace: string, senderId: string | undefined, message: any): void;
 
     /**
      * This function should be called in response to the feedbackstarted event if the application
diff --git a/types/chromecast-caf-receiver/chromecast-caf-receiver-tests.ts b/types/chromecast-caf-receiver/chromecast-caf-receiver-tests.ts
index bff9e9d75f..736fce3537 100644
--- a/types/chromecast-caf-receiver/chromecast-caf-receiver-tests.ts
+++ b/types/chromecast-caf-receiver/chromecast-caf-receiver-tests.ts
@@ -144,6 +144,14 @@ cast.framework.CastReceiverContext.getInstance().addEventListener(
     () => '¡hola!',
 );
 
+// send custom message to specific sender
+cast.framework.CastReceiverContext.getInstance()
+    .sendCustomMessage('custom-namespace', 'sender-id', {});
+
+// broadcast custom message to all connected senders
+cast.framework.CastReceiverContext.getInstance()
+    .sendCustomMessage('custom-namespace', undefined, {});
+
 const loadingError = new cast.framework.events.ErrorEvent(DetailedErrorCode.LOAD_FAILED, 'Loading failed!');
 
 // PlayerManager message interceptors