diff --git a/packages/query-broadcast-client-experimental/src/__tests__/index.test.ts b/packages/query-broadcast-client-experimental/src/__tests__/index.test.ts
index 6e09d8a86e2..02580f16f4f 100644
--- a/packages/query-broadcast-client-experimental/src/__tests__/index.test.ts
+++ b/packages/query-broadcast-client-experimental/src/__tests__/index.test.ts
@@ -1,5 +1,5 @@
 import { QueryClient } from '@tanstack/query-core'
-import { beforeEach, describe, expect, it } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { broadcastQueryClient } from '..'
 import type { QueryCache } from '@tanstack/query-core'
 
@@ -28,4 +28,67 @@ describe('broadcastQueryClient', () => {
     unsubscribe()
     expect(queryCache.hasListeners()).toBe(false)
   })
+
+  describe('postMessage error handling', () => {
+    let unhandledRejections: Array<PromiseRejectionEvent>
+
+    beforeEach(() => {
+      unhandledRejections = []
+      window.addEventListener('unhandledrejection', (e) => {
+        unhandledRejections.push(e)
+        e.preventDefault()
+      })
+    })
+
+    afterEach(() => {
+      window.removeEventListener('unhandledrejection', () => {})
+    })
+
+    it('should not surface DataCloneError as an unhandledrejection', async () => {
+      const unsubscribe = broadcastQueryClient({
+        queryClient,
+        broadcastChannel: 'test_channel_clone_error',
+      })
+
+      // Functions cannot be structured-cloned; setting one as query data
+      // triggers a DataCloneError from postMessage
+      queryClient.setQueryData(['non-cloneable'], () => 'fn')
+
+      // Give the microtask queue a chance to settle
+      await new Promise((resolve) => setTimeout(resolve, 50))
+
+      expect(unhandledRejections).toHaveLength(0)
+      unsubscribe()
+    })
+
+    it('should invoke onBroadcastError with the error and message when postMessage fails', async () => {
+      const cloneError = new DOMException('could not be cloned', 'DataCloneError')
+      const errors: Array<{ error: unknown; queryHash: string }> = []
+
+      const unsubscribe = broadcastQueryClient({
+        queryClient,
+        broadcastChannel: 'test_channel_on_error',
+        onBroadcastError: (error, message) => {
+          errors.push({ error, queryHash: message.queryHash })
+        },
+      })
+
+      // Simulate a postMessage rejection by overriding the channel's postMessage
+      // on the BroadcastChannel prototype so the next call rejects
+      const { BroadcastChannel: BC } = await import('broadcast-channel')
+      const originalPost = BC.prototype.postMessage
+      BC.prototype.postMessage = () => Promise.reject(cloneError)
+
+      queryClient.setQueryData(['key-for-error-test'], 'value')
+
+      await new Promise((resolve) => setTimeout(resolve, 50))
+
+      BC.prototype.postMessage = originalPost
+
+      expect(errors.length).toBeGreaterThan(0)
+      expect(errors[0]!.queryHash).toBe(JSON.stringify(['key-for-error-test']))
+      expect(errors[0]!.error).toBe(cloneError)
+      unsubscribe()
+    })
+  })
 })
diff --git a/packages/query-broadcast-client-experimental/src/index.ts b/packages/query-broadcast-client-experimental/src/index.ts
index e102b3c0b01..bb883bd8671 100644
--- a/packages/query-broadcast-client-experimental/src/index.ts
+++ b/packages/query-broadcast-client-experimental/src/index.ts
@@ -2,16 +2,23 @@ import { BroadcastChannel } from 'broadcast-channel'
 import type { BroadcastChannelOptions } from 'broadcast-channel'
 import type { QueryClient } from '@tanstack/query-core'
 
+type BroadcastMessage =
+  | { type: 'updated'; queryHash: string; queryKey: unknown; state: unknown }
+  | { type: 'removed'; queryHash: string; queryKey: unknown }
+  | { type: 'added'; queryHash: string; queryKey: unknown }
+
 interface BroadcastQueryClientOptions {
   queryClient: QueryClient
   broadcastChannel?: string
   options?: BroadcastChannelOptions
+  onBroadcastError?: (error: unknown, message: BroadcastMessage) => void
 }
 
 export function broadcastQueryClient({
   queryClient,
   broadcastChannel = 'tanstack-query',
   options,
+  onBroadcastError,
 }: BroadcastQueryClientOptions): () => void {
   let transaction = false
   const tx = (cb: () => void) => {
@@ -27,6 +34,19 @@ export function broadcastQueryClient({
 
   const queryCache = queryClient.getQueryCache()
 
+  const safePost = (message: BroadcastMessage) => {
+    channel.postMessage(message).catch((error: unknown) => {
+      if (onBroadcastError) {
+        onBroadcastError(error, message)
+      } else if (process.env.NODE_ENV !== 'production') {
+        console.warn(
+          `[broadcastQueryClient] failed to broadcast "${message.type}" for queryHash "${message.queryHash}":`,
+          error,
+        )
+      }
+    })
+  }
+
   const unsubscribe = queryClient.getQueryCache().subscribe((queryEvent) => {
     if (transaction) {
       return
@@ -37,7 +57,7 @@ export function broadcastQueryClient({
     } = queryEvent
 
     if (queryEvent.type === 'updated' && queryEvent.action.type === 'success') {
-      channel.postMessage({
+      safePost({
         type: 'updated',
         queryHash,
         queryKey,
@@ -46,7 +66,7 @@ export function broadcastQueryClient({
     }
 
     if (queryEvent.type === 'removed' && observers.length > 0) {
-      channel.postMessage({
+      safePost({
         type: 'removed',
         queryHash,
         queryKey,
@@ -54,7 +74,7 @@ export function broadcastQueryClient({
     }
 
     if (queryEvent.type === 'added') {
-      channel.postMessage({
+      safePost({
         type: 'added',
         queryHash,
         queryKey,