diff --git a/scst/include/scst.h b/scst/include/scst.h
index cd74191fd..0c0318f4f 100644
--- a/scst/include/scst.h
+++ b/scst/include/scst.h
@@ -416,6 +416,9 @@ enum scst_exec_context {
 /* Set if session is shutting down */
 #define SCST_SESS_SPH_SHUTDOWN       1
 
+/* Set if session is shutting down */
+#define SCST_SESS_SPH_UNREG_DONE_CALLING 2
+
 /*************************************************************
  ** Session's async (atomic) flags
  *************************************************************/
@@ -783,7 +786,13 @@ struct scst_tgt_template {
 	 * After AEN is sent, target driver must call scst_aen_done() and,
 	 * optionally, scst_set_aen_delivery_status().
 	 *
-	 * This command is expected to be NON-BLOCKING, but can sleep.
+	 * This function is expected to be NON-BLOCKING, but can sleep.
+	 *
+	 * This function must be prepared to handle AENs between calls for the
+	 * corresponding session of scst_unregister_session() and
+	 * unreg_done_fn() callback called or before scst_unregister_session()
+	 * returned, if its called in the blocking mode. AENs for such sessions
+	 * should be ignored.
 	 *
 	 * MUST HAVE, if low-level protocol supports AENs.
 	 */
diff --git a/scst/src/scst_lib.c b/scst/src/scst_lib.c
index e87dafb3e..1ad916371 100644
--- a/scst/src/scst_lib.c
+++ b/scst/src/scst_lib.c
@@ -1326,6 +1326,10 @@ void scst_gen_aen_or_ua(struct scst_tgt_dev *tgt_dev,
 
 	TRACE_ENTRY();
 
+	if ((tgt_dev->sess->init_phase != SCST_SESS_IPH_READY) ||
+	    (tgt_dev->sess->shut_phase != SCST_SESS_SPH_READY))
+		goto out;
+
 	if (tgtt->report_aen != NULL) {
 		struct scst_aen *aen;
 		int rc;
@@ -1488,6 +1492,10 @@ static void scst_report_luns_changed_sess(struct scst_session *sess)
 
 	TRACE_ENTRY();
 
+	if ((sess->init_phase != SCST_SESS_IPH_READY) ||
+	    (sess->shut_phase != SCST_SESS_SPH_READY))
+		goto out;
+
 	TRACE_DBG("REPORTED LUNS DATA CHANGED (sess %p)", sess);
 
 	for (i = 0; i < TGT_DEV_HASH_SIZE; i++) {
@@ -4021,6 +4029,15 @@ void scst_free_session_callback(struct scst_session *sess)
 
 	c = sess->shutdown_compl;
 
+	mutex_lock(&scst_mutex);
+	/*
+	 * Necessary to sync with other threads trying to queue AEN, which
+	 * the target driver will not be able to serve and crash, because after
+	 * unreg_done_fn() called its internal session data will be destroyed.
+	 */
+	sess->shut_phase = SCST_SESS_SPH_UNREG_DONE_CALLING;
+	mutex_unlock(&scst_mutex);
+
 	if (sess->unreg_done_fn) {
 		TRACE_DBG("Calling unreg_done_fn(%p)", sess);
 		sess->unreg_done_fn(sess);