diff --git a/gbproxy/GBProxy_Tests.ttcn b/gbproxy/GBProxy_Tests.ttcn
index 2120fa75b..2797a2ca9 100644
--- a/gbproxy/GBProxy_Tests.ttcn
+++ b/gbproxy/GBProxy_Tests.ttcn
@@ -40,6 +40,9 @@ import from GSM_RR_Types all;
 /* mcc_mnc is 24.008 10.5.5.15 encoded. 262 42 */
 const BcdMccMnc c_mcc_mnc := '262F42'H;
 
+/* 48.016 section 6.1.4.2: The default maximum information field size of 1600 octets shall be supported on the Gb interface */
+const integer max_fr_info_size := 1600;
+
 modulepar {
 	/* IP/port on which we run our internal GSUP/HLR emulation */
 	NSConfigurations mp_nsconfig_sgsn := {
@@ -754,12 +757,13 @@ private function f_TC_ul_unitdata(charstring id) runs on BSSGP_ConnHdlr {
 	var BssgpBvcConfig bvcc := g_pars.pcu[ran_idx].cfg.bvc[0];
 	var integer i;
 
-	for (i := 0; i < 1024; i := i+1) {
+	for (i := 0; i < max_fr_info_size-4; i := i+4) {
 		var octetstring payload := f_rnd_octstring(i);
 		var template (value) PDU_BSSGP pdu_tx := ts_BSSGP_UL_UD(g_pars.tlli, bvcc.cell_id, payload);
 		/* we cannot use pdu_tx as there are some subtle differences in the length field :/ */
 		var template (present) PDU_BSSGP pdu_rx := tr_BSSGP_UL_UD(g_pars.tlli, bvcc.cell_id, payload);
 
+		log("UL-UNITDATA(payload_size=", i);
 		f_pcu2sgsn(pdu_tx, pdu_rx);
 	}
 	setverdict(pass);
@@ -781,7 +785,7 @@ testcase TC_ul_unitdata() runs on test_CT
 private function f_TC_dl_unitdata(charstring id) runs on BSSGP_ConnHdlr {
 	var integer i;
 
-	for (i := 0; i < 1024; i := i+1) {
+	for (i := 0; i < max_fr_info_size-4; i := i+4) {
 		var octetstring payload := f_rnd_octstring(i);
 		var template (value) PDU_BSSGP pdu_tx :=
 			ts_BSSGP_DL_UD(g_pars.tlli, payload, omit, ts_BSSGP_IMSI(g_pars.imsi));
@@ -789,6 +793,7 @@ private function f_TC_dl_unitdata(charstring id) runs on BSSGP_ConnHdlr {
 		var template (present) PDU_BSSGP pdu_rx :=
 			tr_BSSGP_DL_UD(g_pars.tlli, payload, tr_BSSGP_IMSI(g_pars.imsi));
 
+		log("DL-UNITDATA(payload_size=", i);
 		f_sgsn2pcu(pdu_tx, pdu_rx);
 	}
 	setverdict(pass);