diff --git a/library/GTP_Emulation.ttcn b/library/GTP_Emulation.ttcn
index 4ea293c..6297c4f 100644
--- a/library/GTP_Emulation.ttcn
+++ b/library/GTP_Emulation.ttcn
@@ -136,7 +136,11 @@
 	} else if (ischosen(gtp.gtpc_pdu.sgsn_ContextRequest)) {
 		return gtp.gtpc_pdu.sgsn_ContextRequest.imsi.digits;
 	} else if (ischosen(gtp.gtpc_pdu.sgsn_ContextResponse)) {
-		return gtp.gtpc_pdu.sgsn_ContextResponse.imsi.digits;
+		if (ispresent(gtp.gtpc_pdu.sgsn_ContextResponse.imsi.digits)) {
+			return gtp.gtpc_pdu.sgsn_ContextResponse.imsi.digits;
+		} else {
+			return omit;
+		}
 	} else if (ischosen(gtp.gtpc_pdu.forwardRelocationRequest)) {
 		return gtp.gtpc_pdu.forwardRelocationRequest.imsi.digits;
 	} else if (ischosen(gtp.gtpc_pdu.relocationCancelRequest)) {