diff --git a/usr/fileio/common.c b/usr/fileio/common.c
index b1f55051d..32f633b19 100644
--- a/usr/fileio/common.c
+++ b/usr/fileio/common.c
@@ -955,11 +955,11 @@ static void exec_inquiry(struct vdisk_cmd *vcmd)
 		char dev_id_str[17];
 
 		dev_id_num  = gen_dev_id_num(dev);
-		dev_id_len = snprintf(dev_id_str, sizeof(dev_id_str), "%llx",
+		dev_id_len = snprintf(dev_id_str, sizeof(dev_id_str), "%"PRIx64,
 					dev_id_num);
 		if (dev_id_len >= (signed)sizeof(dev_id_str))
 			dev_id_len = sizeof(dev_id_str) - 1;
-		TRACE_DBG("dev_id num %llx, str %s, len %d", dev_id_num,
+		TRACE_DBG("dev_id num %"PRIx64", str %s, len %d", dev_id_num,
 			dev_id_str, dev_id_len);
 		if (0 == cmd->cdb[2]) { /* supported vital product data pages */
 			buf[3] = 3;
diff --git a/usr/fileio/fileio.c b/usr/fileio/fileio.c
index 0949daa01..2e2ab332c 100644
--- a/usr/fileio/fileio.c
+++ b/usr/fileio/fileio.c
@@ -295,7 +295,8 @@ int start(int argc, char **argv)
 			devs[i].file_name, (uint64_t)devs[i].file_size/1024/1024,
 			devs[i].block_size, (uint64_t)devs[i].nblocks);
 
-		snprintf(devs[i].usn, sizeof(devs[i].usn), "%llx", gen_dev_id_num(&devs[i]));
+		snprintf(devs[i].usn, sizeof(devs[i].usn), "%"PRIx64,
+			gen_dev_id_num(&devs[i]));
 		TRACE_DBG("usn %s", devs[i].usn);
 
 		devs[i].scst_usr_fd = open(DEV_USER_PATH DEV_USER_NAME, O_RDWR |