diff --git a/hphp/runtime/ext/asio/asio_external_thread_event.cpp b/hphp/runtime/ext/asio/asio_external_thread_event.cpp
index 56d40f0eb..c519b143a 100644
--- a/hphp/runtime/ext/asio/asio_external_thread_event.cpp
+++ b/hphp/runtime/ext/asio/asio_external_thread_event.cpp
@@ -15,9 +15,9 @@
    +----------------------------------------------------------------------+
 */
 
+#include "hphp/runtime/ext/asio/asio_external_thread_event.h"
 #include <thread>
 #include "hphp/runtime/ext/ext_asio.h"
-#include "hphp/runtime/ext/asio/asio_external_thread_event.h"
 #include "hphp/runtime/ext/asio/asio_session.h"
 
 namespace HPHP {
@@ -32,6 +32,7 @@ AsioExternalThreadEvent::AsioExternalThreadEvent(ObjectData* priv_data)
 void AsioExternalThreadEvent::abandon() {
   assert(m_state.load() == Waiting);
   assert(m_waitHandle->getCount() == 1);
+  m_state.store(Abandoned);
   m_waitHandle->abandon(false);
 }
 
diff --git a/hphp/runtime/ext/asio/asio_external_thread_event.h b/hphp/runtime/ext/asio/asio_external_thread_event.h
index 6c067a45c..00a628d43 100644
--- a/hphp/runtime/ext/asio/asio_external_thread_event.h
+++ b/hphp/runtime/ext/asio/asio_external_thread_event.h
@@ -214,7 +214,11 @@ class AsioExternalThreadEvent {
      * is eventually called.
      */
     virtual ~AsioExternalThreadEvent() {
-      assert(m_state.load() == Finished || m_state.load() == Canceled);
+      assert(
+        m_state.load() == Finished ||
+        m_state.load() == Canceled ||
+        m_state.load() == Abandoned
+      );
     };
 
     /**
@@ -267,6 +271,14 @@ class AsioExternalThreadEvent {
        * eventually calling markAsFinished() that will destruct this object.
        */
       Canceled,
+
+      /**
+       * Web request thread abandoned event before passing to processing thread.
+       *
+       * This object is owned by web request thread, which is trying to abandon
+       * it prior to passing ownership to processing thread.
+       */
+      Abandoned,
     };
 
     AsioSession* m_session;