diff --git a/ggsn_tests/GGSN_Tests.ttcn b/ggsn_tests/GGSN_Tests.ttcn
index 3993ad6..358d756 100644
--- a/ggsn_tests/GGSN_Tests.ttcn
+++ b/ggsn_tests/GGSN_Tests.ttcn
@@ -2096,7 +2096,11 @@
 		/* g_c_seq_nr was increased during f_pdp_ctx_del(), we want a
 		   duplicate. If it was not a duplicate, osmo-ggsn would answer
 		   with a failure since that PDP ctx was already deleted. */
-		g_c_seq_nr := g_c_seq_nr - 1;
+		if (g_c_seq_nr == 0) {
+			g_c_seq_nr := 65535;
+		} else {
+			g_c_seq_nr := g_c_seq_nr - 1;
+		}
 		f_pdp_ctx_del(ctx, '1'B, expect_diameter := false);
 
 		/* Now send a new pdp ctx del (increased seqnum). It should fail with cause "non-existent": */