diff --git a/ggsn_tests/GGSN_Tests.ttcn b/ggsn_tests/GGSN_Tests.ttcn
index ae2a9bf..3993ad6 100644
--- a/ggsn_tests/GGSN_Tests.ttcn
+++ b/ggsn_tests/GGSN_Tests.ttcn
@@ -369,14 +369,14 @@
 	/* send GTP-C for a given context and increment sequence number */
 	function f_send_gtpc(in template Gtp1cUnitdata data) runs on GT_CT {
 		GTPC.send(data);
-		g_c_seq_nr := g_c_seq_nr + 1;
+		g_c_seq_nr := (g_c_seq_nr + 1) mod 65536;
 	}
 
 	/* send GTP-U for a given context and increment sequence number */
 	function f_send_gtpu(inout PdpContext ctx, in octetstring data) runs on GT_CT {
 		if (use_gtpu_txseq) {
 			GTPU.send(ts_GTP1U_GPDU(g_peer_u, g_d_seq_nr, ctx.teid_remote, data));
-			g_d_seq_nr := g_d_seq_nr + 1;
+			g_d_seq_nr := (g_d_seq_nr + 1) mod 65536;
 		} else {
 			GTPU.send(ts_GTP1U_GPDU(g_peer_u, omit, ctx.teid_remote, data));
 		}