diff --git a/src/mme/emm-sm.c b/src/mme/emm-sm.c
index 8fcb552c2..0ce1854cd 100644
--- a/src/mme/emm-sm.c
+++ b/src/mme/emm-sm.c
@@ -882,7 +882,7 @@ void emm_state_authentication(ogs_fsm_t *s, mme_event_t *e)
             OGS_FSM_TRAN(s, &emm_state_exception);
             break;
         case OGS_NAS_EPS_DETACH_REQUEST:
-            ogs_warn("Detach request");
+            ogs_warn("[%s] Detach request", mme_ue->imsi_bcd);
             rv = emm_handle_detach_request(
                     mme_ue, &message->emm.detach_request_from_ue);
             if (rv != OGS_OK) {
@@ -891,7 +891,30 @@ void emm_state_authentication(ogs_fsm_t *s, mme_event_t *e)
                 break;
             }
 
-            mme_send_delete_session_or_detach(mme_ue);
+            if (!MME_UE_HAVE_IMSI(mme_ue)) {
+                ogs_warn("Detach request : Unknown UE");
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (!SECURITY_CONTEXT_IS_VALID(mme_ue)) {
+                ogs_warn("No Security Context : IMSI[%s]", mme_ue->imsi_bcd);
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (MME_P_TMSI_IS_AVAILABLE(mme_ue)) {
+                ogs_assert(OGS_OK == sgsap_send_detach_indication(mme_ue));
+            } else {
+                mme_send_delete_session_or_detach(mme_ue);
+            }
+
             OGS_FSM_TRAN(s, &emm_state_de_registered);
             break;
         default:
@@ -1059,7 +1082,7 @@ void emm_state_security_mode(ogs_fsm_t *s, mme_event_t *e)
             OGS_FSM_TRAN(s, &emm_state_exception);
             break;
         case OGS_NAS_EPS_DETACH_REQUEST:
-            ogs_warn("Detach request");
+            ogs_warn("[%s] Detach request", mme_ue->imsi_bcd);
             rv = emm_handle_detach_request(
                     mme_ue, &message->emm.detach_request_from_ue);
             if (rv != OGS_OK) {
@@ -1068,7 +1091,30 @@ void emm_state_security_mode(ogs_fsm_t *s, mme_event_t *e)
                 break;
             }
 
-            mme_send_delete_session_or_detach(mme_ue);
+            if (!MME_UE_HAVE_IMSI(mme_ue)) {
+                ogs_warn("Detach request : Unknown UE");
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (!SECURITY_CONTEXT_IS_VALID(mme_ue)) {
+                ogs_warn("No Security Context : IMSI[%s]", mme_ue->imsi_bcd);
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (MME_P_TMSI_IS_AVAILABLE(mme_ue)) {
+                ogs_assert(OGS_OK == sgsap_send_detach_indication(mme_ue));
+            } else {
+                mme_send_delete_session_or_detach(mme_ue);
+            }
+
             OGS_FSM_TRAN(s, &emm_state_de_registered);
             break;
         default:
@@ -1257,7 +1303,7 @@ void emm_state_initial_context_setup(ogs_fsm_t *s, mme_event_t *e)
             OGS_FSM_TRAN(s, &emm_state_exception);
             break;
         case OGS_NAS_EPS_DETACH_REQUEST:
-            ogs_warn("Detach request");
+            ogs_warn("[%s] Detach request", mme_ue->imsi_bcd);
             rv = emm_handle_detach_request(
                     mme_ue, &message->emm.detach_request_from_ue);
             if (rv != OGS_OK) {
@@ -1266,7 +1312,30 @@ void emm_state_initial_context_setup(ogs_fsm_t *s, mme_event_t *e)
                 break;
             }
 
-            mme_send_delete_session_or_detach(mme_ue);
+            if (!MME_UE_HAVE_IMSI(mme_ue)) {
+                ogs_warn("Detach request : Unknown UE");
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (!SECURITY_CONTEXT_IS_VALID(mme_ue)) {
+                ogs_warn("No Security Context : IMSI[%s]", mme_ue->imsi_bcd);
+                ogs_assert(OGS_OK ==
+                    nas_eps_send_service_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK));
+                OGS_FSM_TRAN(s, &emm_state_exception);
+                break;
+            }
+
+            if (MME_P_TMSI_IS_AVAILABLE(mme_ue)) {
+                ogs_assert(OGS_OK == sgsap_send_detach_indication(mme_ue));
+            } else {
+                mme_send_delete_session_or_detach(mme_ue);
+            }
+
             OGS_FSM_TRAN(s, &emm_state_de_registered);
             break;
         case OGS_NAS_EPS_SECURITY_MODE_COMPLETE:
diff --git a/src/mme/mme-context.h b/src/mme/mme-context.h
index 182c5bbfe..c455d513e 100644
--- a/src/mme/mme-context.h
+++ b/src/mme/mme-context.h
@@ -539,7 +539,7 @@ struct mme_ue_s {
         ogs_pkbuf_t     *pkbuf;
         ogs_timer_t     *timer;
         uint32_t        retry_count;;
-    } t3413, t3422, t3450, t3460, t3470, t_mobile_reachable, 
+    } t3413, t3422, t3450, t3460, t3470, t_mobile_reachable,
         t_implicit_detach;
 
 #define CLEAR_SERVICE_INDICATOR(__mME) \
diff --git a/src/mme/mme-sm.c b/src/mme/mme-sm.c
index 34596d6de..801df5d2e 100644
--- a/src/mme/mme-sm.c
+++ b/src/mme/mme-sm.c
@@ -307,7 +307,7 @@ void mme_state_operational(ogs_fsm_t *s, mme_event_t *e)
                 ogs_assert(r != OGS_ERROR);
             }
             enb_ue_associate_mme_ue(enb_ue, mme_ue);
-            ogs_debug("Mobile Reachable timer stopped for IMSI[%s]", 
+            ogs_debug("Mobile Reachable timer stopped for IMSI[%s]",
                 mme_ue->imsi_bcd);
             CLEAR_MME_UE_TIMER(mme_ue->t_mobile_reachable);
         }
diff --git a/src/mme/s1ap-handler.c b/src/mme/s1ap-handler.c
index b7024b850..cbc6a831d 100644
--- a/src/mme/s1ap-handler.c
+++ b/src/mme/s1ap-handler.c
@@ -330,7 +330,7 @@ void s1ap_handle_initial_ue_message(mme_enb_t *enb, ogs_s1ap_message_t *message)
                     ogs_assert(r != OGS_ERROR);
                 }
                 enb_ue_associate_mme_ue(enb_ue, mme_ue);
-                ogs_debug("Mobile Reachable timer stopped for IMSI[%s]", 
+                ogs_debug("Mobile Reachable timer stopped for IMSI[%s]",
                     mme_ue->imsi_bcd);
                 CLEAR_MME_UE_TIMER(mme_ue->t_mobile_reachable);
             }