diff --git a/openair3/NAS/NR_UE/nr_nas_msg_sim.c b/openair3/NAS/NR_UE/nr_nas_msg_sim.c
index 43c3b56aa4..2b2d9b08a5 100644
--- a/openair3/NAS/NR_UE/nr_nas_msg_sim.c
+++ b/openair3/NAS/NR_UE/nr_nas_msg_sim.c
@@ -733,16 +733,20 @@ static void generatePduSessionEstablishRequest(int Mod_id, uicc_t * uicc, as_nas
   mm_msg->uplink_nas_transport.pdusessionid = 10;
   mm_msg->uplink_nas_transport.requesttype = 1;
   size += 3;
-  mm_msg->uplink_nas_transport.snssai.length = 4;
+  const bool has_nssai_sd = uicc->nssai_sd != 0xffffff; // 0xffffff means "no SD", TS 23.003
+  const size_t nssai_len = has_nssai_sd ? 4 : 1;
+  mm_msg->uplink_nas_transport.snssai.length = nssai_len;
   //Fixme: it seems there are a lot of memory errors in this: this value was on the stack, 
   // but pushed  in a itti message to another thread
   // this kind of error seems in many places in 5G NAS
-  mm_msg->uplink_nas_transport.snssai.value=calloc(1,4);
+  mm_msg->uplink_nas_transport.snssai.value = calloc(1, nssai_len);
   mm_msg->uplink_nas_transport.snssai.value[0] = uicc->nssai_sst;
-  mm_msg->uplink_nas_transport.snssai.value[1] = (uicc->nssai_sd>>16)&0xFF;
-  mm_msg->uplink_nas_transport.snssai.value[2] = (uicc->nssai_sd>>8)&0xFF; 
-  mm_msg->uplink_nas_transport.snssai.value[3] = (uicc->nssai_sd)&0xFF;
-  size += (1+1+4);
+  if (has_nssai_sd) {
+    mm_msg->uplink_nas_transport.snssai.value[1] = (uicc->nssai_sd >> 16) & 0xFF;
+    mm_msg->uplink_nas_transport.snssai.value[2] = (uicc->nssai_sd >> 8)  & 0xFF;
+    mm_msg->uplink_nas_transport.snssai.value[3] = (uicc->nssai_sd)       & 0xFF;
+  }
+  size += 1 + 1 + nssai_len;
   int dnnSize=strlen(uicc->dnnStr);
   mm_msg->uplink_nas_transport.dnn.value=calloc(1,dnnSize+1);
   mm_msg->uplink_nas_transport.dnn.length = dnnSize + 1;
diff --git a/openair3/UICC/usim_interface.c b/openair3/UICC/usim_interface.c
index 9d6e7c6ccb..78a3f1ee0a 100644
--- a/openair3/UICC/usim_interface.c
+++ b/openair3/UICC/usim_interface.c
@@ -44,7 +44,7 @@ extern uint16_t NB_UE_INST;
       {"sqn",              "USIM sqn\n",           0,         strptr:&uicc->sqnStr,               defstrval:"000000",  TYPE_STRING,    0 }, \
       {"dnn",              "UE dnn (apn)\n",       0,         strptr:&uicc->dnnStr,               defstrval:"oai",     TYPE_STRING,    0 }, \
       {"nssai_sst",            "UE nssai\n",           0,         iptr:&uicc->nssai_sst,             defintval:1,    TYPE_INT,    0 }, \
-      {"nssai_sd",            "UE nssai\n",           0,         iptr:&uicc->nssai_sd,             defintval:1,    TYPE_INT,    0 }, \
+      {"nssai_sd",            "UE nssai\n",           0,         iptr:&uicc->nssai_sd,            defintval:0xffffff,  TYPE_INT,       0 }, \
   };
 
 static uicc_t** uiccArray=NULL;
@@ -73,7 +73,10 @@ uicc_t *init_uicc(char *sectionName) {
   // key, OPc, sqn, amf don't need to be read from the true USIM 
   int ret = config_get( uicc_params,sizeof(uicc_params)/sizeof(paramdef_t),sectionName);
   AssertFatal(ret >= 0, "configuration couldn't be performed for uicc name: %s", sectionName);
-  LOG_I(SIM, "UICC simulation: IMSI=%s, Ki=%s, OPc=%s\n", uicc->imsiStr, uicc->keyStr, uicc->opcStr);
+  LOG_I(SIM,
+        "UICC simulation: IMSI=%s, Ki=%s, OPc=%s, DNN=%s, SST=0x%02x, SD=0x%06x\n",
+        uicc->imsiStr, uicc->keyStr, uicc->opcStr,
+        uicc->dnnStr, uicc->nssai_sst, uicc->nssai_sd);
   to_hex(uicc->keyStr,uicc->key, sizeof(uicc->key) );
   to_hex(uicc->opcStr,uicc->opc, sizeof(uicc->opc) );
   to_hex(uicc->sqnStr,uicc->sqn, sizeof(uicc->sqn) );