diff --git a/protocol/esta/acn/pdu.h b/protocol/esta/acn/pdu.h
index 7ef0774..de600b6 100644
--- a/protocol/esta/acn/pdu.h
+++ b/protocol/esta/acn/pdu.h
@@ -60,7 +60,8 @@ struct pdu_data : public streamable {};
  * @tparam T PDU derived class
  */
 template <class T>
-using Message = std::shared_ptr<T>;
+using Message = std::enable_if_t<std::is_base_of<Pdu, T>::value,
+                                 std::shared_ptr<T>>;
 
 
 /**
@@ -68,7 +69,8 @@ using Message = std::shared_ptr<T>;
  * @tparam T PDU derived class
  */
 template <class T>
-using Handler = std::function<void(Message<T>)>;
+using Handler = std::enable_if_t<std::is_base_of<Pdu, T>::value,
+                                 std::function<void(Message<T>)>>;
 
 
 /**