diff --git a/scst/include/scst.h b/scst/include/scst.h
index 56b4524ca..d67698ab1 100644
--- a/scst/include/scst.h
+++ b/scst/include/scst.h
@@ -403,7 +403,11 @@ struct scst_acg;
 struct scst_acg_dev;
 struct scst_acn;
 
-typedef uint64_t lun_t;
+/*
+ * SCST uses 64-bit numbers to represent LUN's internally. The value
+ * NO_SUCH_LUN is guaranteed to be different of every valid LUN.
+ */
+#define NO_SUCH_LUN ((uint64_t)-1)
 
 typedef enum dma_data_direction scst_data_direction;
 
@@ -1122,7 +1126,7 @@ struct scst_cmd {
 
 	struct scst_tgt_dev *tgt_dev;	/* corresponding device for this cmd */
 
-	lun_t lun;			/* LUN for this cmd */
+	uint64_t lun;			/* LUN for this cmd */
 
 	unsigned long start_time;
 
@@ -1282,7 +1286,7 @@ struct scst_mgmt_cmd {
 	/* Number of completed commands, protected by scst_mcmd_lock */
 	int completed_cmd_count;
 
-	lun_t lun;	/* LUN for this mgmt cmd */
+	uint64_t lun;	/* LUN for this mgmt cmd */
 	/* or (and for iSCSI) */
 	uint64_t tag;	/* tag of the corresponding cmd */
 
@@ -1446,7 +1450,7 @@ struct scst_tgt_dev {
 	struct list_head sess_tgt_dev_list_entry;
 
 	struct scst_device *dev; /* to save extra dereferences */
-	lun_t lun;		 /* to save extra dereferences */
+	uint64_t lun;		 /* to save extra dereferences */
 
 	/* How many cmds alive on this dev in this session */
 	atomic_t tgt_dev_cmd_count;
@@ -1510,7 +1514,7 @@ struct scst_tgt_dev {
  */
 struct scst_acg_dev {
 	struct scst_device *dev; /* corresponding device */
-	lun_t lun;		/* device's LUN in this acg */
+	uint64_t lun;		/* device's LUN in this acg */
 	unsigned int rd_only_flag:1; /* if != 0, then read only */
 	struct scst_acg *acg;	/* parent acg */
 
diff --git a/scst/src/scst_lib.c b/scst/src/scst_lib.c
index a1da67ac9..7701951f0 100644
--- a/scst/src/scst_lib.c
+++ b/scst/src/scst_lib.c
@@ -192,7 +192,7 @@ int scst_get_cmd_abnormal_done_state(const struct scst_cmd *cmd)
 
 	TRACE_ENTRY();
 
-	switch(cmd->state) {
+	switch (cmd->state) {
 	case SCST_CMD_STATE_INIT_WAIT:
 	case SCST_CMD_STATE_INIT:
 	case SCST_CMD_STATE_PRE_PARSE:
@@ -215,7 +215,7 @@ void scst_set_cmd_abnormal_done_state(struct scst_cmd *cmd)
 	TRACE_ENTRY();
 
 #ifdef EXTRACHECKS
-	switch(cmd->state) {
+	switch (cmd->state) {
 	case SCST_CMD_STATE_PRE_XMIT_RESP:
 	case SCST_CMD_STATE_XMIT_RESP:
 	case SCST_CMD_STATE_FINISHED:
@@ -347,7 +347,7 @@ void scst_init_mem_lim(struct scst_mem_lim *mem_lim)
 EXPORT_SYMBOL(scst_init_mem_lim);
 
 struct scst_acg_dev *scst_alloc_acg_dev(struct scst_acg *acg,
-	struct scst_device *dev, lun_t lun)
+					struct scst_device *dev, uint64_t lun)
 {
 	struct scst_acg_dev *res;
 
@@ -746,8 +746,8 @@ void scst_sess_free_tgt_devs(struct scst_session *sess)
 }
 
 /* The activity supposed to be suspended and scst_mutex held */
-int scst_acg_add_dev(struct scst_acg *acg, struct scst_device *dev, lun_t lun,
-	int read_only)
+int scst_acg_add_dev(struct scst_acg *acg, struct scst_device *dev,
+		     uint64_t lun, int read_only)
 {
 	int res = 0;
 	struct scst_acg_dev *acg_dev;
@@ -1922,9 +1922,9 @@ EXPORT_SYMBOL(scst_get_cdb_info);
  * (see SAM-2, Section 4.12.3 page 40)
  * Supports 2 types of lun unpacking: peripheral and logical unit.
  */
-lun_t scst_unpack_lun(const uint8_t *lun, int len)
+uint64_t scst_unpack_lun(const uint8_t *lun, int len)
 {
-	lun_t res = (lun_t)-1;
+	uint64_t res = NO_SUCH_LUN;
 	int address_method;
 
 	TRACE_ENTRY();
diff --git a/scst/src/scst_priv.h b/scst/src/scst_priv.h
index b6efbbe33..310fcf98b 100644
--- a/scst/src/scst_priv.h
+++ b/scst/src/scst_priv.h
@@ -286,8 +286,8 @@ int scst_sess_alloc_tgt_devs(struct scst_session *sess);
 void scst_sess_free_tgt_devs(struct scst_session *sess);
 void scst_nexus_loss(struct scst_tgt_dev *tgt_dev);
 
-int scst_acg_add_dev(struct scst_acg *acg, struct scst_device *dev, lun_t lun,
-	int read_only);
+int scst_acg_add_dev(struct scst_acg *acg, struct scst_device *dev,
+		     uint64_t lun, int read_only);
 int scst_acg_remove_dev(struct scst_acg *acg, struct scst_device *dev);
 
 int scst_acg_add_name(struct scst_acg *acg, const char *name);
@@ -359,7 +359,7 @@ int scst_alloc_space(struct scst_cmd *cmd);
 void scst_release_space(struct scst_cmd *cmd);
 void scst_scsi_op_list_init(void);
 
-lun_t scst_unpack_lun(const uint8_t *lun, int len);
+uint64_t scst_unpack_lun(const uint8_t *lun, int len);
 
 struct scst_cmd *__scst_find_cmd_by_tag(struct scst_session *sess,
 	uint64_t tag);
diff --git a/scst/src/scst_targ.c b/scst/src/scst_targ.c
index 3818851f1..fb9346d00 100644
--- a/scst/src/scst_targ.c
+++ b/scst/src/scst_targ.c
@@ -249,7 +249,7 @@ void scst_cmd_init_done(struct scst_cmd *cmd, int pref_context)
 
 	spin_unlock_irqrestore(&sess->sess_list_lock, flags);
 
-	if (unlikely(cmd->lun == (lun_t)-1)) {
+	if (unlikely(cmd->lun == NO_SUCH_LUN)) {
 		PRINT_ERROR("Wrong LUN %d, finishing cmd", -1);
 		scst_set_cmd_error(cmd,
 			   SCST_LOAD_SENSE(scst_sense_lun_not_supported));
@@ -4821,7 +4821,7 @@ int scst_rx_mgmt_fn(struct scst_session *sess,
 
 	if (params->lun_set) {
 		mcmd->lun = scst_unpack_lun(params->lun, params->lun_len);
-		if (mcmd->lun == (lun_t)-1)
+		if (mcmd->lun == NO_SUCH_LUN)
 			goto out_free;
 		mcmd->lun_set = 1;
 	}