diff --git a/mme/LTE_CryptoFunctions.ttcn b/mme/LTE_CryptoFunctions.ttcn
index 18a3755..f0ea990 100644
--- a/mme/LTE_CryptoFunctions.ttcn
+++ b/mme/LTE_CryptoFunctions.ttcn
@@ -40,6 +40,8 @@
 
 external function f_kdf_nh(in OCT16 kasme, in OCT32 sync_inp) return OCT32;
 
+external function f_kdf_nas_token(in OCT16 kasme, in integer ul_count) return OCT32;
+
 /*********************************************************************************
  * mid-level API
  *********************************************************************************/