diff --git a/client/concurrentqueue.h b/client/concurrentqueue.h
index 074dc2f2..c31c7d03 100644
--- a/client/concurrentqueue.h
+++ b/client/concurrentqueue.h
@@ -688,6 +688,9 @@ template<typename T, typename Traits = ConcurrentQueueDefaultTraits>
 class ConcurrentQueue
 {
 public:
+    struct ExplicitProducer;
+    struct ImplicitProducer;
+
 	typedef ::moodycamel::ProducerToken producer_token_t;
 	typedef ::moodycamel::ConsumerToken consumer_token_t;