diff --git a/openair3/NAS/NR_UE/5GS/tests/nas_lib_test.c b/openair3/NAS/NR_UE/5GS/tests/nas_lib_test.c
index a73ee9b2be..2ccf78fa59 100644
--- a/openair3/NAS/NR_UE/5GS/tests/nas_lib_test.c
+++ b/openair3/NAS/NR_UE/5GS/tests/nas_lib_test.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <arpa/inet.h>
 #include "common/utils/ds/byte_array.h"
+#include "RegistrationAccept.h"
 #include "fgs_service_request.h"
 #include "fgmm_service_accept.h"
 #include "fgmm_service_reject.h"
@@ -26,6 +27,65 @@ static bool eq_service_request(const fgs_service_request_msg_t *a, const fgs_ser
   return result;
 }
 
+/** @brief Test regression of NAS Registration Accept decoding
+ *         This test verifies that the NAS Registration Accept message
+ *         is correctly decoded. It decodes a message as it received from
+ *         the OAI CN5G and compares the output with the expected Registration Accept structure.
+ *         The purpose of this regression test is to ensure that changes
+ *         to the NAS decoder do not break the existing decoding behavior with OAI CN5G */
+static void test_regression_registration_accept(void)
+{
+  // Registration Accept message
+  registration_accept_msg orig = {
+      .guti = malloc_or_fail(sizeof(*orig.guti)),
+      .result = 0x01,
+      .nas_allowed_nssai[0].sst = 0x01,
+      .nas_allowed_nssai[1].sst = 0x02,
+      .nas_allowed_nssai[2].sst = 0x03,
+      .num_allowed_slices = 3,
+      .config_nssai[0].sst = 0x01,
+      .config_nssai[1].sst = 0x02,
+      .config_nssai[2].sst = 0x03,
+      .num_configured_slices = 3,
+  };
+
+  orig.guti->guti.typeofidentity = FGS_MOBILE_IDENTITY_5G_GUTI;
+  orig.guti->guti.amfpointer = 0x01;
+  orig.guti->guti.amfregionid = 0x02;
+  orig.guti->guti.amfsetid = 0x01;
+  orig.guti->guti.mccdigit1 = 0x00;
+  orig.guti->guti.mccdigit2 = 0x00;
+  orig.guti->guti.mccdigit3 = 0x01;
+  orig.guti->guti.mncdigit1 = 0x00;
+  orig.guti->guti.mncdigit2 = 0x01;
+  orig.guti->guti.mncdigit3 = 0x0F;
+  orig.guti->guti.tmsi = 0xb0207806;
+  orig.guti->guti.spare = 0b1111;
+  orig.guti->guti.oddeven = 0;
+
+  // Encoded Registration Accept message from OAI CN5G
+  uint8_t cn5g_msg[] = {0x01, 0x01, // Registration Result
+                        0x77, 0x00, 0x0B, 0xF2, 0x00, 0xF1, 0x10, // 5G-GUTI
+                        0x02, 0x00, 0x41, 0xB0, 0x20, 0x78, 0x06, // 5G-GUTI
+                        0x15, 0x06, 0x01, 0x01, 0x01, 0x02, 0x01, 0x03, // Allowed N-NSSAI
+                        0x31, 0x06, 0x01, 0x01, 0x01, 0x02, 0x01, 0x03}; // Configured N-NSSAI
+
+  // Decode NAS Registration Accept
+  int encoded_length;
+  registration_accept_msg decoded = {0};
+  byte_array_t ba = {.buf = cn5g_msg, .len = sizeof(cn5g_msg)};
+  encoded_length = decode_registration_accept(&decoded, ba);
+  AssertFatal(encoded_length >= 0, "encode_fgs_service_request() failed\n");
+
+  // Compare the raw encoded buffer with expected encoded data
+  bool ret = eq_fgmm_registration_accept(&orig, &decoded);
+  AssertFatal(ret, "Encoding mismatch!\n");
+
+  // Free dynamic allocated memory
+  free_fgmm_registration_accept(&orig);
+  free_fgmm_registration_accept(&decoded);
+}
+
 /**
  * @brief Test NAS Service Request enc/dec
  */
@@ -172,6 +232,7 @@ static void test_service_reject(void)
 
 int main()
 {
+  test_regression_registration_accept();
   test_service_request();
   test_service_accept();
   test_service_reject();