diff --git a/lib/test/upper/rlc_um_test.cc b/lib/test/upper/rlc_um_test.cc
index f572128eb..4730516eb 100644
--- a/lib/test/upper/rlc_um_test.cc
+++ b/lib/test/upper/rlc_um_test.cc
@@ -94,6 +94,29 @@ public:
   uint32_t expected_sdu_len;
 };
 
+srslte::rlc_config_t make_rlc_cnfg_default(uint32_t sn)
+{
+  rlc_config_t cnfg;
+  cnfg.rlc_mode        = rlc_mode_t::um;
+  cnfg.um.t_reordering = 5;
+  if (sn == 10) {
+    cnfg.um.rx_sn_field_length = rlc_umd_sn_size_t::size10bits;
+    cnfg.um.rx_window_size     = 512;
+    cnfg.um.rx_mod             = 1024;
+    cnfg.um.tx_sn_field_length = rlc_umd_sn_size_t::size10bits;
+    cnfg.um.tx_mod             = 1024;
+  } else if (sn == 5) {
+    cnfg.um.rx_sn_field_length = rlc_umd_sn_size_t::size5bits;
+    cnfg.um.rx_window_size     = 16;
+    cnfg.um.rx_mod             = 32;
+    cnfg.um.tx_sn_field_length = rlc_umd_sn_size_t::size5bits;
+    cnfg.um.tx_mod             = 32;
+  } else {
+    printf("NOT supported\n");
+  }
+  return cnfg;
+}
+
 int basic_test()
 {
   srslte::log_filter log1("RLC_UM_1");
@@ -109,7 +132,7 @@ int basic_test()
   rlc_um rlc1(&log1, 3, &tester, &tester, &timers);
   rlc_um rlc2(&log2, 3, &tester, &tester, &timers);
 
-  rlc_config_t cnfg;
+  rlc_config_t cnfg          = make_rlc_cnfg_default(10);
   cnfg.rlc_mode              = rlc_mode_t::um;
   cnfg.um.t_reordering       = 5;
   cnfg.um.rx_sn_field_length = rlc_umd_sn_size_t::size10bits;
@@ -179,14 +202,7 @@ int loss_test()
   rlc_um rlc1(&log1, 3, &tester, &tester, &timers);
   rlc_um rlc2(&log2, 3, &tester, &tester, &timers);
 
-  rlc_config_t cnfg;
-  cnfg.rlc_mode              = rlc_mode_t::um;
-  cnfg.um.t_reordering       = 5;
-  cnfg.um.rx_sn_field_length = rlc_umd_sn_size_t::size10bits;
-  cnfg.um.rx_window_size     = 512;
-  cnfg.um.rx_mod             = 1024;
-  cnfg.um.tx_sn_field_length = rlc_umd_sn_size_t::size10bits;
-  cnfg.um.tx_mod             = 1024;
+  rlc_config_t cnfg = make_rlc_cnfg_default(10);
 
   rlc1.configure(cnfg);
   rlc2.configure(cnfg);
@@ -319,14 +335,7 @@ int reassmble_test()
   rlc_um rlc1(&log1, 3, &tester, &tester, &timers);
   rlc_um rlc2(&log2, 3, &tester, &tester, &timers);
 
-  rlc_config_t cnfg;
-  cnfg.rlc_mode              = rlc_mode_t::um;
-  cnfg.um.t_reordering       = 5;
-  cnfg.um.rx_sn_field_length = rlc_umd_sn_size_t::size5bits;
-  cnfg.um.rx_window_size     = 16;
-  cnfg.um.rx_mod             = 32;
-  cnfg.um.tx_sn_field_length = rlc_umd_sn_size_t::size5bits;
-  cnfg.um.tx_mod             = 32;
+  rlc_config_t cnfg = make_rlc_cnfg_default(5);
 
   rlc1.configure(cnfg);
   rlc2.configure(cnfg);
@@ -435,14 +444,7 @@ int reassmble_test2()
   rlc_um rlc1(&log1, 3, &tester, &tester, &timers);
   rlc_um rlc2(&log2, 3, &tester, &tester, &timers);
 
-  rlc_config_t cnfg;
-  cnfg.rlc_mode              = rlc_mode_t::um;
-  cnfg.um.t_reordering       = 5;
-  cnfg.um.rx_sn_field_length = rlc_umd_sn_size_t::size5bits;
-  cnfg.um.rx_window_size     = 16;
-  cnfg.um.rx_mod             = 32;
-  cnfg.um.tx_sn_field_length = rlc_umd_sn_size_t::size5bits;
-  cnfg.um.tx_mod             = 32;
+  rlc_config_t cnfg = make_rlc_cnfg_default(5);
 
   rlc1.configure(cnfg);
   rlc2.configure(cnfg);