diff --git a/TCAP/src/ITU/tcap_cco_server.erl b/TCAP/src/ITU/tcap_cco_server.erl
index 72a6c76..1e5f78b 100644
--- a/TCAP/src/ITU/tcap_cco_server.erl
+++ b/TCAP/src/ITU/tcap_cco_server.erl
@@ -277,12 +277,19 @@ terminate_ISMs([{_Id, ISM}|Tail]) ->
 	gen_fsm:send_event(ISM, terminate),
 	terminate_ISMs(Tail).
 
+undef2empty(undefined) ->
+	[];
+undef2empty(asn1_NOVALUE) ->
+	[];
+undef2empty(Foo) ->
+	Foo.
+
 % Convert from user-visible primitive records to asn1ct-generated record
 uprim_to_asn_rec(Uprim) when is_record(Uprim, 'TC-INVOKE') ->
 	{invoke, #'Invoke'{invokeId = inv_id_to_asn_rec(Uprim#'TC-INVOKE'.invokeID),
 		  linkedId = inv_id_to_asn_rec(Uprim#'TC-INVOKE'.linkedID),
 		  opcode = osmo_util:asn_val(Uprim#'TC-INVOKE'.operation),
-		  argument = osmo_util:asn_val(Uprim#'TC-INVOKE'.parameters)}};
+		  argument = undef2empty(Uprim#'TC-INVOKE'.parameters)}};
 uprim_to_asn_rec(#'TC-RESULT-NL'{invokeID = InvId, operation = Op,
 				 parameters = Params}) ->
 	ResRes = #'ReturnResult_result'{opcode = osmo_util:asn_val(Op),