diff --git a/fr/FR_Tests.ttcn b/fr/FR_Tests.ttcn
index b7a56c3..65029c1 100644
--- a/fr/FR_Tests.ttcn
+++ b/fr/FR_Tests.ttcn
@@ -276,7 +276,7 @@
 		var integer ran_index := 0;
 		var template (value) PDU_LLC llc_tx;
 		var template (present) PDU_LLC llc_rx_exp;
-		var octetstring llc_payload := f_rnd_octstring(f_rnd_int(max_llc_payload_len));
+		var octetstring llc_payload := f_rnd_octstring_rnd_len(max_llc_payload_len);
 		var PDU_LLC llc_rx;
 		timer T := 5.0;
 
diff --git a/library/Osmocom_Types.ttcn b/library/Osmocom_Types.ttcn
index b698a2e..2edec36 100644
--- a/library/Osmocom_Types.ttcn
+++ b/library/Osmocom_Types.ttcn
@@ -65,6 +65,11 @@
 	return float2int(rnd()*int2float(max));
 }
 
+/* return random integer 1 <= ret < max */
+function f_rnd_int_nonzero(integer max) return integer {
+	return float2int(1.0 + rnd()*int2float(max-1));
+}
+
 /* return hexstring composed of random digits */
 function f_rnd_hexstring(in integer len, in integer max := 16) return hexstring {
 	var integer i;
@@ -85,6 +90,11 @@
 	return ret;
 }
 
+/* return ocetstring composed of random bytes, at least 1, maximum 'maxlen' bytes long */
+function f_rnd_octstring_rnd_len(in integer maxlen) return octetstring {
+	return f_rnd_octstring(f_rnd_int_nonzero(maxlen));
+}
+
 /* return bitstring composed of random bits */
 function f_rnd_bitstring(in integer len) return bitstring {
 	var octetstring oct := f_rnd_octstring(len / 8 + 1);
diff --git a/pcap-client/OPCAP_CLIENT_Tests.ttcn b/pcap-client/OPCAP_CLIENT_Tests.ttcn
index e9fe406..1efc343 100644
--- a/pcap-client/OPCAP_CLIENT_Tests.ttcn
+++ b/pcap-client/OPCAP_CLIENT_Tests.ttcn
@@ -144,7 +144,7 @@
 		var octetstring udp_payload;
 
 		/* we assume 1400 is low enough to avoid IP fragmentation */
-		udp_payload := f_rnd_octstring(f_rnd_int(1400));
+		udp_payload := f_rnd_octstring_rnd_len(1400);
 		f_trafic_pkt_ab(udp_payload);
 
 		f_opcap_exp_udp(udp_payload, 0);
@@ -173,7 +173,7 @@
 		var octetstring udp_payload;
 
 		/* we assume 1400 is low enough to avoid IP fragmentation */
-		udp_payload := f_rnd_octstring(f_rnd_int(1400));
+		udp_payload := f_rnd_octstring_rnd_len(1400);
 		f_trafic_pkt_ab(udp_payload);
 
 		/* expect packet to arrive on both simulated servers */
diff --git a/remsim/RemsimClient_Tests.ttcn b/remsim/RemsimClient_Tests.ttcn
index d7d6bc7..219573c 100644
--- a/remsim/RemsimClient_Tests.ttcn
+++ b/remsim/RemsimClient_Tests.ttcn
@@ -299,8 +299,8 @@
 			integer count := 100, integer i := 0) runs on client_test_CT
 {
 	for (var integer j := 0; j < count; j := j+1) {
-		var octetstring c_apdu := f_rnd_octstring(f_rnd_int(270));
-		var octetstring r_apdu := f_rnd_octstring(f_rnd_int(270));
+		var octetstring c_apdu := f_rnd_octstring_rnd_len(270);
+		var octetstring r_apdu := f_rnd_octstring_rnd_len(270);
 		f_client2bank(cslot, bslot, c_apdu, i:=i);
 		f_bank2client(bslot, cslot, r_apdu, i:=i);
 	}
@@ -345,8 +345,8 @@
 
 	f_set_atr(cslot, '3B9F96801FC78031A073BE21136743200718000001A5'O, i:=1);
 
-	var octetstring c_apdu := f_rnd_octstring(f_rnd_int(270));
-	var octetstring r_apdu := f_rnd_octstring(f_rnd_int(270));
+	var octetstring c_apdu := f_rnd_octstring_rnd_len(270);
+	var octetstring r_apdu := f_rnd_octstring_rnd_len(270);
 	/* Send C-APDU from correct ClientId/Slot to simulated bankd */
 	f_client2bank(cslot, bslot, c_apdu, i:=1);
 	/* respond with R-APDU from correct bankId/Slot but stating wrong ClientId */
@@ -372,8 +372,8 @@
 
 	f_set_atr(cslot, '3B9F96801FC78031A073BE21136743200718000001A5'O, i:=1);
 
-	var octetstring c_apdu := f_rnd_octstring(f_rnd_int(270));
-	var octetstring r_apdu := f_rnd_octstring(f_rnd_int(270));
+	var octetstring c_apdu := f_rnd_octstring_rnd_len(270);
+	var octetstring r_apdu := f_rnd_octstring_rnd_len(270);
 	/* Send C-APDU from correct ClientId/Slot to simulated bankd */
 	f_client2bank(cslot, bslot, c_apdu, i:=1);
 	/* respond with R-APDU from wrong bankId but stating correct ClientId */
diff --git a/sccp/SCCP_Tests_RAW.ttcn b/sccp/SCCP_Tests_RAW.ttcn
index 5013ddf..fd6bad9 100644
--- a/sccp/SCCP_Tests_RAW.ttcn
+++ b/sccp/SCCP_Tests_RAW.ttcn
@@ -182,7 +182,7 @@
 testcase TC_udt_without_cr_cc() runs on SCCP_Test_RAW_CT {
 	var SCCP_PAR_Address calling, called;
 	var SCCP_MTP3_TRANSFERind rx;
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 
 	/* Keep recommended ratio of T(iar) >= T(ias)*2, but anyway no IT
 	   should be received in this case. */
@@ -215,7 +215,7 @@
 testcase TC_tiar_timeout() runs on SCCP_Test_RAW_CT {
 	var SCCP_PAR_Address calling, called;
 	var OCT3 remote_lref;
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 
 	/* Set T(iar) in sccp_demo_user low enough that it will trigger before other side
 	   has time to keep alive with a T(ias). Keep recommended ratio of
@@ -320,7 +320,7 @@
 /* Test if the IUT SCCP code processes an XUDT [treat it like UDT] and answers back. */
 testcase TC_process_rx_xudt() runs on SCCP_Test_RAW_CT {
 	var SCCP_PAR_Address calling, called;
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 
 	f_init_raw(mp_sccp_cfg[0]);
 	f_sleep(1.0);
diff --git a/stp/STP_Tests.ttcn b/stp/STP_Tests.ttcn
index 004af05..ac45b1d 100644
--- a/stp/STP_Tests.ttcn
+++ b/stp/STP_Tests.ttcn
@@ -73,7 +73,7 @@
 	f_M3UA_asp_up_act(0, omit, omit); // TODO: rctx
 
 	/* send a well-formed, encoded SCCP message via M3UA */
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 	var SCCP_PAR_Address called := valueof(ts_SccpAddr_GT('1234'H));
 	var SCCP_PAR_Address calling := valueof(ts_SccpAddr_GT('5678'H));
 	var PDU_SCCP sccp := valueof(ts_SCCP_UDT(called, calling, data));
@@ -105,7 +105,7 @@
 	f_M3UA_asp_up_act(0, omit, omit); // TODO: rctx
 
 	/* send a well-formed, encoded SCCP message via IPA */
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 	var SCCP_PAR_Address called := valueof(ts_SccpAddr_GT('1234'H));
 	var SCCP_PAR_Address calling := valueof(ts_SccpAddr_GT('5678'H));
 	var PDU_SCCP sccp := valueof(ts_SCCP_UDT(called, calling, data));
@@ -137,7 +137,7 @@
 	f_M3UA_asp_up_act(0, omit, omit); // TODO: rctx
 
 	/* send a well-formed, encoded SCCP message via IPA */
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 	var SCCP_PAR_Address called := valueof(ts_SccpAddr_GT('1234'H));
 	var SCCP_PAR_Address calling := valueof(ts_SccpAddr_GT('5678'H));
 	var PDU_SCCP sccp := valueof(ts_SCCP_UDT(called, calling, data));
@@ -173,7 +173,7 @@
 	f_M3UA_asp_up_act(0, omit, omit); // TODO: rctx
 
 	/* send a well-formed, encoded SCCP message via IPA */
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 	var SCCP_PAR_Address called := valueof(ts_SccpAddr_GT('1234'H));
 	var SCCP_PAR_Address calling := valueof(ts_SccpAddr_GT('5678'H));
 	var PDU_SCCP sccp := valueof(ts_SCCP_UDT(called, calling, data));
diff --git a/stp/STP_Tests_M3UA.ttcn b/stp/STP_Tests_M3UA.ttcn
index 31bab93..08fc9c9 100644
--- a/stp/STP_Tests_M3UA.ttcn
+++ b/stp/STP_Tests_M3UA.ttcn
@@ -407,7 +407,7 @@
 				integer idx_rx, template (omit) OCT4 rctx_receiver, OCT4 pc_rx,
 				OCT1 si := '23'O, OCT1 ni := '00'O, OCT1 mp := '00'O, OCT1 sls := '00'O)
 runs on RAW_M3UA_CT {
-	var octetstring data := f_rnd_octstring(f_rnd_int(100));
+	var octetstring data := f_rnd_octstring_rnd_len(100);
 	f_M3UA_send(idx_tx, ts_M3UA_DATA(rctx_sender,
 					 ts_M3UA_protocol_data(pc_tx, pc_rx, si, ni, mp, sls, data)), 1);
 	f_M3UA_exp(idx_rx, tr_M3UA_DATA(rctx_receiver,
@@ -482,7 +482,7 @@
 	const integer iter_per_asp := 5;
 	var integer num_rx[NR_M3UA] := { 0, 0, 0 };
 	for (i := 0; i < 2*iter_per_asp; i := i+1) {
-		var octetstring data := f_rnd_octstring(f_rnd_int(100));
+		var octetstring data := f_rnd_octstring_rnd_len(100);
 		var template (value) M3UA_Protocol_Data tx_pd;
 		var template (present) M3UA_Protocol_Data rx_pd;
 		tx_pd := ts_M3UA_protocol_data(pc_sender, pc_receiver, '23'O, '00'O, '00'O, '00'O, data);
@@ -533,7 +533,7 @@
 
 	/* verify traffic is routed from sender to new receiver */
 	for (i := 0; i < 10; i := i+1) {
-		var octetstring data := f_rnd_octstring(f_rnd_int(100));
+		var octetstring data := f_rnd_octstring_rnd_len(100);
 		var template (value) M3UA_Protocol_Data tx_pd;
 		var template (present) M3UA_Protocol_Data rx_pd;
 		tx_pd := ts_M3UA_protocol_data(pc_sender, pc_receiver, '23'O, '00'O, '00'O, '00'O, data);