diff --git a/library/RAN_Emulation.ttcnpp b/library/RAN_Emulation.ttcnpp
index 891de09..b54d6e4 100644
--- a/library/RAN_Emulation.ttcnpp
+++ b/library/RAN_Emulation.ttcnpp
@@ -1444,8 +1444,17 @@
 }
 
 /* helper function for clients to register their IMSI/TMSI */
-function f_ran_register_imsi(hexstring imsi, OCT4 tmsi)
+function f_ran_register_imsi(hexstring imsi, template (omit) OCT4 tmsi_or_omit)
 runs on RAN_ConnHdlr {
+	var OCT4 tmsi;
+
+	/* Resolve omit to a special reserved value */
+	if (istemplatekind(tmsi_or_omit, "omit")) {
+		tmsi := 'FFFFFFFF'O;
+	} else {
+		tmsi := valueof(tmsi_or_omit);
+	}
+
 	BSSAP_PROC.call(RAN_register_imsi:{imsi, tmsi, self}) {
 		[] BSSAP_PROC.getreply(RAN_register_imsi:{?,?,?}) {};
 	}