diff --git a/src/applications/model/onoff-application.cc b/src/applications/model/onoff-application.cc
index 543ad3c94..06911ea23 100644
--- a/src/applications/model/onoff-application.cc
+++ b/src/applications/model/onoff-application.cc
@@ -82,9 +82,11 @@ OnOffApplication::GetTypeId (void)
                    UintegerValue (0),
                    MakeUintegerAccessor (&OnOffApplication::m_maxBytes),
                    MakeUintegerChecker<uint64_t> ())
-    .AddAttribute ("Protocol", "The type of protocol to use.",
+    .AddAttribute ("Protocol", "The type of protocol to use. This should be "
+                   "a subclass of ns3::SocketFactory",
                    TypeIdValue (UdpSocketFactory::GetTypeId ()),
                    MakeTypeIdAccessor (&OnOffApplication::m_tid),
+                   // This should check for SocketFactory as a parent
                    MakeTypeIdChecker ())
     .AddTraceSource ("Tx", "A new packet is created and is sent",
                      MakeTraceSourceAccessor (&OnOffApplication::m_txTrace),