diff --git a/srsenb/hdr/stack/rrc/rrc_ue.h b/srsenb/hdr/stack/rrc/rrc_ue.h
index 9b574cb90..feac3600a 100644
--- a/srsenb/hdr/stack/rrc/rrc_ue.h
+++ b/srsenb/hdr/stack/rrc/rrc_ue.h
@@ -68,7 +68,7 @@ public:
   enum class conn_request_result_t { success, error_mme_not_connected, error_unknown_rnti };
 
   /// Possible causes for the RRC to transition to the idle state.
-  enum class rrc_idle_transition_cause { release, timeout, radio_conn_with_ue_lost };
+  enum class rrc_idle_transition_cause { release, timeout, radio_conn_with_ue_lost, msg3_timeout, unspecified };
 
   void handle_rrc_con_req(asn1::rrc::rrc_conn_request_s* msg);
   void handle_rrc_con_setup_complete(asn1::rrc::rrc_conn_setup_complete_s* msg, srsran::unique_byte_buffer_t pdu);
diff --git a/srsenb/src/stack/rrc/rrc_ue.cc b/srsenb/src/stack/rrc/rrc_ue.cc
index b6cb146e6..56b729201 100644
--- a/srsenb/src/stack/rrc/rrc_ue.cc
+++ b/srsenb/src/stack/rrc/rrc_ue.cc
@@ -126,12 +126,20 @@ void rrc::ue::activity_timer_expired(activity_timeout_type_t type)
             ue_cell_list.get_ue_cc_idx(UE_PCELL_CC_IDX)->cell_common->enb_cc_idx,
             static_cast<unsigned>(rrc_idle_transition_cause::radio_conn_with_ue_lost),
             rnti);
+      } else if (type == MSG3_RX_TIMEOUT) {
+        // MSG3 timeout, no need to notify S1AP, just remove UE
+        parent->rem_user_thread(rnti);
+        event_logger::get().log_rrc_disconnect(ue_cell_list.get_ue_cc_idx(UE_PCELL_CC_IDX)->cell_common->enb_cc_idx,
+                                               static_cast<unsigned>(rrc_idle_transition_cause::msg3_timeout),
+                                               rnti);
       } else {
-        parent->s1ap->user_release(rnti, asn1::s1ap::cause_radio_network_opts::unspecified);
-        event_logger::get().log_rrc_disconnect(
-            ue_cell_list.get_ue_cc_idx(UE_PCELL_CC_IDX)->cell_common->enb_cc_idx,
-            static_cast<unsigned>(rrc_idle_transition_cause::radio_conn_with_ue_lost),
-            rnti);
+        // Unhandled activity timeout, just remove UE and log an error
+        parent->rem_user_thread(rnti);
+        event_logger::get().log_rrc_disconnect(ue_cell_list.get_ue_cc_idx(UE_PCELL_CC_IDX)->cell_common->enb_cc_idx,
+                                               static_cast<unsigned>(rrc_idle_transition_cause::msg3_timeout),
+                                               rnti);
+        parent->logger.error(
+            "Unhandled reason for activity timer expiration. rnti=0x%x, cause %d", rnti, static_cast<unsigned>(type));
       }
     } else {
       if (rnti != SRSRAN_MRNTI) {