Index: uspace/drv/usbmast/main.c
===================================================================
--- uspace/drv/usbmast/main.c	(revision cf002dbf0c969fa30210f823ac7b17cae5996095)
+++ uspace/drv/usbmast/main.c	(revision c372e032f5e68c630fb49e061ddf9910bccbbdd4)
@@ -107,15 +107,5 @@
 	    (size_t) dev->pipes[BULK_OUT_EP].descriptor->max_packet_size);
 
-	int lun_count = usb_massstor_get_max_lun(dev);
-	/* Return value:
-	 * rc < 0 => device does not know this request, only single LUN
-	 *     could be present
-	 * rc >= 0 - the rc is the maximum LUN, thus count is +1
-	 */
-	if (lun_count < 0) {
-		lun_count = 1;
-	} else {
-		lun_count++;
-	}
+	size_t lun_count = usb_masstor_get_lun_count(dev);
 
 	usb_massstor_inquiry_result_t inquiry;
@@ -127,5 +117,6 @@
 	}
 
-	usb_log_info("Mass storage `%s': `%s' by `%s' is %s (%s), %d LUN(s).\n",
+	usb_log_info("Mass storage `%s': " \
+	    "`%s' by `%s' is %s (%s), %zu LUN(s).\n",
 	    dev->ddf_dev->name,
 	    inquiry.product_and_revision, inquiry.vendor_id,
Index: uspace/drv/usbmast/mast.c
===================================================================
--- uspace/drv/usbmast/mast.c	(revision cf002dbf0c969fa30210f823ac7b17cae5996095)
+++ uspace/drv/usbmast/mast.c	(revision c372e032f5e68c630fb49e061ddf9910bccbbdd4)
@@ -173,6 +173,9 @@
 /** Get max LUN of a mass storage device.
  *
+ * @see usb_masstor_get_lun_count
+ *
  * @warning Error from this command does not necessarily indicate malfunction
  * of the device. Device does not need to support this request.
+ * You shall rather use usb_masstor_get_lun_count.
  *
  * @param dev Mass storage device.
@@ -195,4 +198,24 @@
 }
 
+/** Get number of LUNs supported by mass storage device.
+ *
+ * @warning This function hides any error during the request
+ * (typically that shall not be a problem).
+ *
+ * @param dev Mass storage device.
+ * @return Number of LUNs.
+ */
+size_t usb_masstor_get_lun_count(usb_device_t *dev)
+{
+	int max_lun = usb_massstor_get_max_lun(dev);
+	if (max_lun < 0) {
+		max_lun = 1;
+	} else {
+		max_lun++;
+	}
+
+	return (size_t) max_lun;
+}
+
 /**
  * @}
Index: uspace/drv/usbmast/mast.h
===================================================================
--- uspace/drv/usbmast/mast.h	(revision cf002dbf0c969fa30210f823ac7b17cae5996095)
+++ uspace/drv/usbmast/mast.h	(revision c372e032f5e68c630fb49e061ddf9910bccbbdd4)
@@ -62,4 +62,5 @@
 void usb_massstor_reset_recovery(usb_device_t *, size_t, size_t);
 int usb_massstor_get_max_lun(usb_device_t *);
+size_t usb_masstor_get_lun_count(usb_device_t *);
 int usb_massstor_inquiry(usb_device_t *, size_t, size_t,
     usb_massstor_inquiry_result_t *);