diff --git a/src/message_bus.h b/src/message_bus.h
index 4be39fca..6dae3fbf 100644
--- a/src/message_bus.h
+++ b/src/message_bus.h
@@ -83,15 +83,6 @@ namespace etl
 
   public:
 
-    //*******************************************
-    /// Constructor.
-    //*******************************************
-    imessage_bus(router_list_t& list)
-      : imessage_router(etl::imessage_router::MESSAGE_BUS),
-        router_list(list)
-    {
-    }
-
     using etl::imessage_router::receive;
 
     //*******************************************
@@ -299,6 +290,17 @@ namespace etl
       return router_list.clear();
     }
 
+  protected:
+
+    //*******************************************
+    /// Constructor.
+    //*******************************************
+    imessage_bus(router_list_t& list)
+      : imessage_router(etl::imessage_router::MESSAGE_BUS),
+        router_list(list)
+    {
+    }
+
   private:
 
     //*******************************************