diff --git a/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.c b/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.c
index dfcb1fce94..ed0de936f5 100644
--- a/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.c
+++ b/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.c
@@ -33,13 +33,11 @@
 #include <string.h>
 #include <stdint.h>
 #include "conversions.h"
-#include "TLVEncoder.h"
-#include "TLVDecoder.h"
 #include "RegistrationAccept.h"
-#include "assertions.h"
 #include "fgs_nas_utils.h"
 #include "common/utils/utils.h"
 #include "ds/byte_array.h"
+#include "fgmm_lib.h"
 
 #define IEI_5G_GUTI 0x77
 #define FGS_REGISTRATION_RESULT_LEN 2
@@ -128,56 +126,65 @@ static int decode_nssai_ie(nr_nas_msg_snssai_t *nssai, const uint8_t *buf)
   return decoded;
 }
 
-int decode_registration_accept(registration_accept_msg *registration_accept, const uint8_t *buffer, uint32_t len)
+size_t decode_registration_accept(registration_accept_msg *registration_accept, const byte_array_t buffer)
 {
   int dec = 0;
-  const uint8_t *end = buffer + len;
+  byte_array_t ba = buffer; // local copy of buffer
+
+  if (ba.len < REGISTRATION_ACCEPT_MIN_LEN) {
+    PRINT_NAS_ERROR("Registration Accept decoding failed: invalid buffer length\n");
+    return -1;
+  }
 
   // 5GS registration result (Mandatory)
-  byte_array_t ba = {.buf = buffer, .len = len};
   if ((dec = decode_fgs_registration_result(registration_accept, ba)) < 0)
-    return dec;
-  buffer += dec;
+    return -1;
+  UPDATE_BYTE_ARRAY(ba, dec);
 
-  if (buffer < end && *buffer == IEI_5G_GUTI) {
+  // 5G-GUTI (Optional)
+  if (ba.len > 0 && ba.buf[0] == IEI_5G_GUTI) {
     registration_accept->guti = calloc_or_fail(1, sizeof(*registration_accept->guti));
-    if ((dec = decode_5gs_mobile_identity(registration_accept->guti, IEI_5G_GUTI, buffer, end - buffer)) < 0) {
+    if ((dec = decode_5gs_mobile_identity(registration_accept->guti, IEI_5G_GUTI, ba.buf, ba.len)) < 0) {
       PRINT_NAS_ERROR("Failed to decode 5GS Mobile Identity in Registration Accept\n");
       return -1;
     }
-    buffer += dec;
+    UPDATE_BYTE_ARRAY(ba, dec);
   }
 
-  // Allowed NSSAI (O)
-  /* Optional Presence IEs */
-  while (buffer < end) {
-    const int iei = *buffer++;
+  // Decode other Optional IEs
+  while (ba.len > 0) {
+    uint8_t iei = ba.buf[0];
+    UPDATE_BYTE_ARRAY(ba, 1);
+
     switch (iei) {
 
       case 0x15: // allowed NSSAI
-        dec = decode_nssai_ie(registration_accept->nas_allowed_nssai, buffer);
-        buffer += dec;
+        dec = decode_nssai_ie(registration_accept->nas_allowed_nssai, ba.buf);
+        UPDATE_BYTE_ARRAY(ba, dec);
         break;
 
       case 0x31: // configured NSSAI
-        dec = decode_nssai_ie(registration_accept->config_nssai, buffer);
-        buffer += dec;
+        dec = decode_nssai_ie(registration_accept->config_nssai, ba.buf);
+        UPDATE_BYTE_ARRAY(ba, dec);
         break;
 
       default:
-        dec = *buffer++; // content length + 1 byte (Length IE)
-        buffer += dec;
+        dec = ba.buf[0] + 1; // content length + 1 byte (Length IE)
+        UPDATE_BYTE_ARRAY(ba, dec);
         break;
     }
   }
-  return len;
+  if(ba.len != 0) {
+    PRINT_NAS_ERROR("Failed to decode registration accept: ba.len = %ld\n", ba.len);
+    return -1;
+  }
+  return buffer.len;
 }
 
 int encode_registration_accept(const registration_accept_msg *registration_accept, uint8_t *buffer, uint32_t len)
 {
   int encoded = 0;
 
-  LOG_FUNC_IN;
   byte_array_t ba = {.buf = buffer, .len = len};
   encoded += encode_fgs_registration_result(ba, registration_accept);
 
@@ -188,6 +195,5 @@ int encode_registration_accept(const registration_accept_msg *registration_accep
     encoded += mi_enc;
   }
 
-  // todo ,Encoding optional fields
-  LOG_FUNC_RETURN(encoded);
+  return encoded;
 }
diff --git a/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.h b/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.h
index 5f444e95f9..8c044603de 100644
--- a/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.h
+++ b/openair3/NAS/NR_UE/5GS/5GMM/MSG/RegistrationAccept.h
@@ -35,6 +35,7 @@
 #include "SecurityHeaderType.h"
 #include "MessageType.h"
 #include "FGSMobileIdentity.h"
+#include "ds/byte_array.h"
 
 #ifndef REGISTRATION_ACCEPT_H_
 #define REGISTRATION_ACCEPT_H_
@@ -45,6 +46,8 @@ typedef enum {
   FGS_REGISTRATION_RESULT_3GPP_AND_NON_3GPP = 3
 } fgs_registration_result_t;
 
+#define NAS_MAX_NUMBER_SLICES 8
+
 // 9.11.3.37 of 3GPP TS 24.501
 typedef struct {
   int sst;
@@ -66,13 +69,13 @@ typedef struct registration_accept_msg_tag {
   bool sms_allowed;
   // 5G-GUTI (Optional)
   FGSMobileIdentity *guti;
-  // Allowed NSSAI (O)
-  nr_nas_msg_snssai_t nas_allowed_nssai[8];
-  // Configured NSSAI (O)
-  nr_nas_msg_snssai_t config_nssai[8];
+  // Allowed NSSAI (Optional)
+  nr_nas_msg_snssai_t nas_allowed_nssai[NAS_MAX_NUMBER_SLICES];
+  // Configured NSSAI (Optional)
+  nr_nas_msg_snssai_t config_nssai[NAS_MAX_NUMBER_SLICES];
 } registration_accept_msg;
 
-int decode_registration_accept(registration_accept_msg *registrationaccept, const uint8_t *buffer, uint32_t len);
+size_t decode_registration_accept(registration_accept_msg *registrationaccept, const byte_array_t buffer);
 
 int encode_registration_accept(const registration_accept_msg *registrationaccept, uint8_t *buffer, uint32_t len);
 
diff --git a/openair3/NAS/NR_UE/nr_nas_msg.c b/openair3/NAS/NR_UE/nr_nas_msg.c
index 08003bbcba..5ee233172c 100644
--- a/openair3/NAS/NR_UE/nr_nas_msg.c
+++ b/openair3/NAS/NR_UE/nr_nas_msg.c
@@ -1460,7 +1460,8 @@ static void handle_registration_accept(nr_ue_nas_t *nas, const uint8_t *pdu_buff
   }
   pdu_buffer += decoded;
   // plain payload
-  if ((decoded = decode_registration_accept(&msg, pdu_buffer, end - pdu_buffer)) < 0) {
+  const byte_array_t ba = {.buf = (uint8_t *)pdu_buffer, .len = end - pdu_buffer};
+  if ((decoded = decode_registration_accept(&msg, ba)) < 0) {
     LOG_E(NAS, "Failed to decode NAS Registration Accept\n");
     return;
   }