diff --git a/include/gui/BufferQueueProducer.h b/include/gui/BufferQueueProducer.h
index c619a11..ed1056a 100644
--- a/include/gui/BufferQueueProducer.h
+++ b/include/gui/BufferQueueProducer.h
@@ -203,6 +203,16 @@
     // since the previous buffer might have already been acquired.
     sp<Fence> mLastQueueBufferFence;
 
+    // Take-a-ticket system for ensuring that onFrame* callbacks are called in
+    // the order that frames are queued. While the BufferQueue lock
+    // (mCore->mMutex) is held, a ticket is retained by the producer. After
+    // dropping the BufferQueue lock, the producer must wait on the condition
+    // variable until the current callback ticket matches its retained ticket.
+    Mutex mCallbackMutex;
+    int mNextCallbackTicket; // Protected by mCore->mMutex
+    int mCurrentCallbackTicket; // Protected by mCallbackMutex
+    Condition mCallbackCondition;
+
 }; // class BufferQueueProducer
 
 } // namespace android