diff --git a/pcu/GPRS_TBF.ttcn b/pcu/GPRS_TBF.ttcn
index f946f29..3794410 100644
--- a/pcu/GPRS_TBF.ttcn
+++ b/pcu/GPRS_TBF.ttcn
@@ -14,6 +14,7 @@
 import from GSM_Types all;
 import from Osmocom_Types all;
 import from General_Types all;
+import from Misc_Helpers all;
 import from RLCMAC_CSN1_Types all;
 import from RLCMAC_Types all;
 import from RLCMAC_Templates all;
@@ -409,8 +410,9 @@
 }
 
 function f_dl_tbf_is_in_window(integer bsn) return boolean {
-	setverdict(fail, "pleaes implement me");
-	mtc.stop;
+	Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
+				"please implement me");
+	return false;
 }
 
 function f_dl_tbf_is_received(inout DlTbfState ds, integer bsn) return boolean {