diff --git a/src/internal/queue/event.ts b/src/internal/queue/event.ts
index dc19a34de..671fd0397 100644
--- a/src/internal/queue/event.ts
+++ b/src/internal/queue/event.ts
@@ -21,6 +21,16 @@ export interface BasePayload {
 
 const { pgQueueEnable, region, isMultitenant } = getConfig()
 
+function withPayloadVersion<TPayload extends BasePayload>(
+  payload: TPayload,
+  version: string
+): TPayload {
+  return {
+    ...payload,
+    $version: payload.$version ?? version,
+  }
+}
+
 export type StaticThis<T extends Event<any>> = BaseEventConstructor<T>
 
 interface BaseEventConstructor<Base extends Event<any>> {
@@ -101,19 +111,20 @@ export class Event<T extends Omit<BasePayload, '$version'>> {
 
     return Queue.getInstance().insert(
       messages.map((message) => {
-        const sendOptions = (this.getSendOptions(message.payload) as PgBoss.JobInsert) || {}
-        if (!message.payload.$version) {
-          ;(message.payload as (typeof message)['payload']).$version = this.version
-        }
+        const payloadWithVersion = withPayloadVersion(
+          message.payload as (typeof message)['payload'],
+          this.version
+        )
+        const sendOptions = (this.getSendOptions(payloadWithVersion) as PgBoss.JobInsert) || {}
 
-        if (message.payload.scheduleAt) {
-          sendOptions.startAfter = new Date(message.payload.scheduleAt)
+        if (payloadWithVersion.scheduleAt) {
+          sendOptions.startAfter = new Date(payloadWithVersion.scheduleAt)
         }
 
         return {
           ...sendOptions,
           name: this.getQueueName(),
-          data: message.payload,
+          data: payloadWithVersion,
           deadLetter: this.deadLetterQueueName(),
         }
       })
@@ -125,10 +136,7 @@ export class Event<T extends Omit<BasePayload, '$version'>> {
     payload: Omit<T['payload'], '$version'>,
     opts?: SendOptions & { tnx?: Knex }
   ) {
-    if (!payload.$version) {
-      ;(payload as T['payload']).$version = this.version
-    }
-    const that = new this(payload)
+    const that = new this(withPayloadVersion(payload as T['payload'], this.version))
     return that.send(opts)
   }
 
@@ -136,10 +144,7 @@ export class Event<T extends Omit<BasePayload, '$version'>> {
     this: StaticThis<T>,
     payload: Omit<T['payload'], '$version'>
   ) {
-    if (!payload.$version) {
-      ;(payload as T['payload']).$version = this.version
-    }
-    const that = new this(payload)
+    const that = new this(withPayloadVersion(payload as T['payload'], this.version))
     return that.invoke()
   }
 
@@ -148,10 +153,7 @@ export class Event<T extends Omit<BasePayload, '$version'>> {
     payload: Omit<T['payload'], '$version'>,
     options?: SendOptions & { sendWhenError?: (error: unknown) => boolean }
   ) {
-    if (!payload.$version) {
-      ;(payload as T['payload']).$version = this.version
-    }
-    const that = new this(payload)
+    const that = new this(withPayloadVersion(payload as T['payload'], this.version))
     return that.invokeOrSend(options)
   }
 
diff --git a/src/test/event.test.ts b/src/test/event.test.ts
new file mode 100644
index 000000000..35a4368e7
--- /dev/null
+++ b/src/test/event.test.ts
@@ -0,0 +1,141 @@
+'use strict'
+
+type EventModule = typeof import('../internal/queue/event')
+type QueueModule = typeof import('../internal/queue/queue')
+
+type TestPayload = {
+  name: string
+  tenant: {
+    ref: string
+    host: string
+  }
+  reqId?: string
+  scheduleAt?: Date
+}
+
+async function loadQueueModules(opts?: { pgQueueEnable?: boolean }) {
+  jest.resetModules()
+
+  const configModule = await import('../config')
+  configModule.getConfig({ reload: true })
+  configModule.mergeConfig({
+    pgQueueEnable: opts?.pgQueueEnable ?? false,
+  })
+
+  const eventModule = (await import('../internal/queue/event')) as EventModule
+  const queueModule = (await import('../internal/queue/queue')) as QueueModule
+
+  return { eventModule, queueModule }
+}
+
+function defineTestEvent(EventBase: EventModule['Event']) {
+  return class TestEvent extends EventBase<TestPayload> {
+    static readonly version = 'v-test'
+    protected static queueName = 'test-event'
+  }
+}
+
+function createPayload(overrides: Partial<TestPayload> = {}): TestPayload {
+  return {
+    name: 'test-object',
+    tenant: {
+      ref: 'test-tenant',
+      host: 'localhost',
+    },
+    reqId: 'req-123',
+    ...overrides,
+  }
+}
+
+describe('Event payload versioning', () => {
+  afterEach(() => {
+    jest.restoreAllMocks()
+    jest.resetModules()
+  })
+
+  it('does not mutate payloads passed to static send', async () => {
+    const { eventModule } = await loadQueueModules()
+    const TestEvent = defineTestEvent(eventModule.Event)
+    const payload = createPayload()
+
+    jest.spyOn(TestEvent.prototype, 'send').mockImplementation(function (
+      this: InstanceType<typeof TestEvent>
+    ) {
+      expect(this.payload.$version).toBe('v-test')
+      return Promise.resolve('queued')
+    })
+
+    await TestEvent.send(payload)
+
+    expect(payload).toEqual(createPayload())
+    expect(payload).not.toHaveProperty('$version')
+  })
+
+  it('does not mutate payloads passed to static invoke', async () => {
+    const { eventModule } = await loadQueueModules()
+    const TestEvent = defineTestEvent(eventModule.Event)
+    const payload = createPayload()
+
+    jest.spyOn(TestEvent.prototype, 'invoke').mockImplementation(function (
+      this: InstanceType<typeof TestEvent>
+    ) {
+      expect(this.payload.$version).toBe('v-test')
+      return Promise.resolve(null)
+    })
+
+    await TestEvent.invoke(payload)
+
+    expect(payload).toEqual(createPayload())
+    expect(payload).not.toHaveProperty('$version')
+  })
+
+  it('does not mutate payloads passed to static invokeOrSend', async () => {
+    const { eventModule } = await loadQueueModules()
+    const TestEvent = defineTestEvent(eventModule.Event)
+    const payload = createPayload()
+
+    jest.spyOn(TestEvent.prototype, 'invokeOrSend').mockImplementation(function (
+      this: InstanceType<typeof TestEvent>
+    ) {
+      expect(this.payload.$version).toBe('v-test')
+      return Promise.resolve(null)
+    })
+
+    await TestEvent.invokeOrSend(payload)
+
+    expect(payload).toEqual(createPayload())
+    expect(payload).not.toHaveProperty('$version')
+  })
+
+  it('does not mutate message payloads when batching', async () => {
+    const { eventModule, queueModule } = await loadQueueModules({ pgQueueEnable: true })
+    const TestEvent = defineTestEvent(eventModule.Event)
+    const payload = createPayload({ scheduleAt: new Date('2026-04-07T10:00:00.000Z') })
+    const insert = jest.fn().mockResolvedValue('job-id')
+
+    jest
+      .spyOn(queueModule.Queue, 'getInstance')
+      .mockReturnValue({ insert } as unknown as ReturnType<typeof queueModule.Queue.getInstance>)
+
+    const message = new TestEvent(payload)
+
+    await TestEvent.batchSend([message])
+
+    expect(payload).toEqual(createPayload({ scheduleAt: new Date('2026-04-07T10:00:00.000Z') }))
+    expect(payload).not.toHaveProperty('$version')
+    expect(insert).toHaveBeenCalledWith([
+      expect.objectContaining({
+        name: 'test-event',
+        deadLetter: 'test-event-dead-letter',
+        data: expect.objectContaining({
+          $version: 'v-test',
+          name: 'test-object',
+          tenant: expect.objectContaining({
+            ref: 'test-tenant',
+          }),
+        }),
+        startAfter: new Date('2026-04-07T10:00:00.000Z'),
+      }),
+    ])
+  })
+})