diff --git a/hphp/runtime/ext/asio/asio_external_thread_event.cpp b/hphp/runtime/ext/asio/asio_external_thread_event.cpp
index 2d5f66121..ba9e76415 100644
--- a/hphp/runtime/ext/asio/asio_external_thread_event.cpp
+++ b/hphp/runtime/ext/asio/asio_external_thread_event.cpp
@@ -23,10 +23,10 @@
 namespace HPHP {
 ///////////////////////////////////////////////////////////////////////////////
 
-AsioExternalThreadEvent::AsioExternalThreadEvent()
+AsioExternalThreadEvent::AsioExternalThreadEvent(ObjectData* priv_data)
     : m_session(AsioSession::Get()),
       m_state(Waiting) {
-  m_waitHandle = c_ExternalThreadEventWaitHandle::Create(this);
+  m_waitHandle = c_ExternalThreadEventWaitHandle::Create(this, priv_data);
 }
 
 void AsioExternalThreadEvent::abandon() {
diff --git a/hphp/runtime/ext/asio/asio_external_thread_event.h b/hphp/runtime/ext/asio/asio_external_thread_event.h
index aaa2aec76..dcbcd11cb 100644
--- a/hphp/runtime/ext/asio/asio_external_thread_event.h
+++ b/hphp/runtime/ext/asio/asio_external_thread_event.h
@@ -195,7 +195,15 @@ class AsioExternalThreadEvent {
     virtual void unserialize(TypedValue* result) const = 0;
 
   protected:
-    AsioExternalThreadEvent();
+    /**
+     * Construct AsioExternalThreadEvent
+     *
+     * Subclass may optionally pass a PHP object (usually defined by extension)
+     * that can be accessed during unserialize() via getPrivData(). A reference
+     * to the object will be held while associated ExternalThreadEventWaitHandle
+     * object is in WAITING state.
+     */
+    explicit AsioExternalThreadEvent(ObjectData* priv_data = nullptr);
 
     /**
      * Destruct AsioExternalThreadEvent
@@ -222,6 +230,17 @@ class AsioExternalThreadEvent {
      */
     void markAsFinished();
 
+    /**
+     * Get private PHP data needed for unserialization.
+     *
+     * This function obtains private data stored by constructor. It may be
+     * called only from the unserialize() implementation.
+     */
+    ObjectData* getPrivData() const {
+      assert(m_state.load() == Finished);
+      return m_waitHandle->getPrivData();
+    }
+
   private:
     enum state_t : uint32_t {
       /**
diff --git a/hphp/runtime/ext/asio/external_thread_event_wait_handle.cpp b/hphp/runtime/ext/asio/external_thread_event_wait_handle.cpp
index 8565bac09..ee97fbe80 100644
--- a/hphp/runtime/ext/asio/external_thread_event_wait_handle.cpp
+++ b/hphp/runtime/ext/asio/external_thread_event_wait_handle.cpp
@@ -62,16 +62,17 @@ void c_ExternalThreadEventWaitHandle::t___construct() {
   throw e;
 }
 
-c_ExternalThreadEventWaitHandle* c_ExternalThreadEventWaitHandle::Create(AsioExternalThreadEvent* event) {
+c_ExternalThreadEventWaitHandle* c_ExternalThreadEventWaitHandle::Create(AsioExternalThreadEvent* event, ObjectData* priv_data) {
   c_ExternalThreadEventWaitHandle* wh = NEWOBJ(c_ExternalThreadEventWaitHandle);
-  wh->initialize(event);
+  wh->initialize(event, priv_data);
   return wh;
 }
 
-void c_ExternalThreadEventWaitHandle::initialize(AsioExternalThreadEvent* event) {
+void c_ExternalThreadEventWaitHandle::initialize(AsioExternalThreadEvent* event, ObjectData* priv_data) {
   // this wait handle is owned by existence of unprocessed event
   incRefCount();
   m_event = event;
+  m_privData = priv_data;
 
   setState(STATE_WAITING);
   if (isInContext()) {
@@ -114,6 +115,7 @@ void c_ExternalThreadEventWaitHandle::process() {
   // event is processed, destroy it, unregister sweepable and decref ownership
   m_event->release();
   m_event = nullptr;
+  m_privData = nullptr;
   unregister();
   decRefObj(this);
 }
diff --git a/hphp/runtime/ext/ext_asio.h b/hphp/runtime/ext/ext_asio.h
index e2d70af3d..32dde17ea 100644
--- a/hphp/runtime/ext/ext_asio.h
+++ b/hphp/runtime/ext/ext_asio.h
@@ -439,10 +439,11 @@ class c_ExternalThreadEventWaitHandle : public c_WaitableWaitHandle, public Swee
   public: void t___construct();
 
  public:
-  static c_ExternalThreadEventWaitHandle* Create(AsioExternalThreadEvent* event);
+  static c_ExternalThreadEventWaitHandle* Create(AsioExternalThreadEvent* event, ObjectData* priv_data);
 
   c_ExternalThreadEventWaitHandle* getNextToProcess() { assert(getState() == STATE_WAITING); return m_nextToProcess; }
   void setNextToProcess(c_ExternalThreadEventWaitHandle* next) { assert(getState() == STATE_WAITING); m_nextToProcess = next; }
+  ObjectData* getPrivData() { return m_privData.get(); }
   void setIndex(uint32_t ete_idx) { assert(getState() == STATE_WAITING); m_index = ete_idx; }
 
   void abandon(bool sweeping);
@@ -452,10 +453,11 @@ class c_ExternalThreadEventWaitHandle : public c_WaitableWaitHandle, public Swee
   void exitContext(context_idx_t ctx_idx);
 
  private:
-  void initialize(AsioExternalThreadEvent* event);
+  void initialize(AsioExternalThreadEvent* event, ObjectData* priv_data);
 
   c_ExternalThreadEventWaitHandle* m_nextToProcess;
   AsioExternalThreadEvent* m_event;
+  Object m_privData;
   uint32_t m_index;
 
   static const uint8_t STATE_WAITING  = 3;