diff --git a/lib/include/srslte/asn1/liblte_mme.h b/lib/include/srslte/asn1/liblte_mme.h
index 6cc91871d..e5f13615b 100644
--- a/lib/include/srslte/asn1/liblte_mme.h
+++ b/lib/include/srslte/asn1/liblte_mme.h
@@ -692,6 +692,7 @@ LIBLTE_ERROR_ENUM liblte_mme_unpack_drx_parameter_ie(uint8** ie_ptr, LIBLTE_MME_
 #define LIBLTE_MME_EMM_CAUSE_SECURITY_MODE_REJECTED_UNSPECIFIED 0x18
 #define LIBLTE_MME_EMM_CAUSE_NOT_AUTHORIZED_FOR_THIS_CSG 0x19
 #define LIBLTE_MME_EMM_CAUSE_NON_EPS_AUTHENTICATION_UNACCEPTABLE 0x1A
+#define LIBLTE_MME_EMM_CAUSE_REQUESTED_SERVICE_OPTION_NOT_AUTHORIZED 0x23
 #define LIBLTE_MME_EMM_CAUSE_CS_SERVICE_TEMPORARILY_NOT_AVAILABLE 0x27
 #define LIBLTE_MME_EMM_CAUSE_NO_EPS_BEARER_CONTEXT_ACTIVATED 0x28
 #define LIBLTE_MME_EMM_CAUSE_SEMANTICALLY_INCORRECT_MESSAGE 0x5F
diff --git a/srsue/src/stack/upper/nas.cc b/srsue/src/stack/upper/nas.cc
index d56b48701..7a5436c6b 100644
--- a/srsue/src/stack/upper/nas.cc
+++ b/srsue/src/stack/upper/nas.cc
@@ -1119,8 +1119,19 @@ void nas::parse_attach_reject(uint32_t lcid, unique_byte_buffer_t pdu)
     t3410.stop();
   }
 
+  // 5.5.1.2.5
+  if (attach_rej.emm_cause == LIBLTE_MME_EMM_CAUSE_ILLEGAL_UE ||
+      attach_rej.emm_cause == LIBLTE_MME_EMM_CAUSE_ILLEGAL_ME ||
+      attach_rej.emm_cause == LIBLTE_MME_EMM_CAUSE_REQUESTED_SERVICE_OPTION_NOT_AUTHORIZED) {
+    // delete security context
+    have_guti = false;
+    have_ctxt = false;
+    ctxt      = {};
+  }
+
+  // TODO: handle other relevant reject causes
+
   enter_emm_deregistered();
-  // TODO: Command RRC to release?
 }
 
 void nas::parse_authentication_request(uint32_t lcid, unique_byte_buffer_t pdu, const uint8_t sec_hdr_type)