diff --git a/ports/stm32/usbd_msc_interface.h b/ports/stm32/usbd_msc_interface.h
index 411c707cab..9d25a72a3a 100644
--- a/ports/stm32/usbd_msc_interface.h
+++ b/ports/stm32/usbd_msc_interface.h
@@ -26,8 +26,6 @@
 #ifndef MICROPY_INCLUDED_STM32_USBD_MSC_INTERFACE_H
 #define MICROPY_INCLUDED_STM32_USBD_MSC_INTERFACE_H
 
-#define USBD_MSC_MAX_LUN (2)
-
 extern const USBD_StorageTypeDef usbd_msc_fops;
 
 void usbd_msc_init_lu(size_t lu_n, const void *lu_data);
diff --git a/ports/stm32/usbdev/class/inc/usbd_cdc_msc_hid.h b/ports/stm32/usbdev/class/inc/usbd_cdc_msc_hid.h
index d934f4676c..d6c38bbd07 100644
--- a/ports/stm32/usbdev/class/inc/usbd_cdc_msc_hid.h
+++ b/ports/stm32/usbdev/class/inc/usbd_cdc_msc_hid.h
@@ -34,6 +34,9 @@
 #define MSC_MEDIA_PACKET            (2048) // was 8192; how low can it go whilst still working?
 #define HID_DATA_FS_MAX_PACKET_SIZE (64) // endpoint IN & OUT packet size
 
+// Maximum number of LUN that can be exposed on the MSC interface
+#define USBD_MSC_MAX_LUN (2)
+
 // Need to define here for BOT and SCSI layers
 #define MSC_IN_EP     (0x81)
 #define MSC_OUT_EP    (0x01)
@@ -78,8 +81,8 @@ typedef struct {
   uint8_t                  scsi_sense_head;
   uint8_t                  scsi_sense_tail;
   
-  uint16_t                 scsi_blk_size;
-  uint32_t                 scsi_blk_nbr;
+  uint16_t                 scsi_blk_size[USBD_MSC_MAX_LUN];
+  uint32_t                 scsi_blk_nbr[USBD_MSC_MAX_LUN];
   
   uint32_t                 scsi_blk_addr_in_blks;
   uint32_t                 scsi_blk_len;
diff --git a/ports/stm32/usbdev/class/src/usbd_msc_scsi.c b/ports/stm32/usbdev/class/src/usbd_msc_scsi.c
index d0413b758a..2eb716ccde 100644
--- a/ports/stm32/usbdev/class/src/usbd_msc_scsi.c
+++ b/ports/stm32/usbdev/class/src/usbd_msc_scsi.c
@@ -247,7 +247,7 @@ static int8_t SCSI_ReadCapacity10(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_
 {
   USBD_MSC_BOT_HandleTypeDef *hmsc = &((usbd_cdc_msc_hid_state_t*)pdev->pClassData)->MSC_BOT_ClassData;
 
-  if(hmsc->bdev_ops->GetCapacity(lun, &hmsc->scsi_blk_nbr, &hmsc->scsi_blk_size) != 0)
+  if(hmsc->bdev_ops->GetCapacity(lun, &hmsc->scsi_blk_nbr[lun], &hmsc->scsi_blk_size[lun]) != 0)
   {
     SCSI_SenseCode(pdev,
                    lun,
@@ -258,15 +258,17 @@ static int8_t SCSI_ReadCapacity10(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_
   else
   {
 
-    hmsc->bot_data[0] = (uint8_t)((hmsc->scsi_blk_nbr - 1) >> 24);
-    hmsc->bot_data[1] = (uint8_t)((hmsc->scsi_blk_nbr - 1) >> 16);
-    hmsc->bot_data[2] = (uint8_t)((hmsc->scsi_blk_nbr - 1) >>  8);
-    hmsc->bot_data[3] = (uint8_t)(hmsc->scsi_blk_nbr - 1);
+    uint32_t blk_nbr = hmsc->scsi_blk_nbr[lun];
+    hmsc->bot_data[0] = (uint8_t)((blk_nbr - 1) >> 24);
+    hmsc->bot_data[1] = (uint8_t)((blk_nbr - 1) >> 16);
+    hmsc->bot_data[2] = (uint8_t)((blk_nbr - 1) >>  8);
+    hmsc->bot_data[3] = (uint8_t)(blk_nbr - 1);
 
-    hmsc->bot_data[4] = (uint8_t)(hmsc->scsi_blk_size >>  24);
-    hmsc->bot_data[5] = (uint8_t)(hmsc->scsi_blk_size >>  16);
-    hmsc->bot_data[6] = (uint8_t)(hmsc->scsi_blk_size >>  8);
-    hmsc->bot_data[7] = (uint8_t)(hmsc->scsi_blk_size);
+    uint32_t blk_size = hmsc->scsi_blk_size[lun];
+    hmsc->bot_data[4] = (uint8_t)(blk_size >> 24);
+    hmsc->bot_data[5] = (uint8_t)(blk_size >> 16);
+    hmsc->bot_data[6] = (uint8_t)(blk_size >> 8);
+    hmsc->bot_data[7] = (uint8_t)(blk_size);
 
     hmsc->bot_data_length = 8;
     return 0;
@@ -516,7 +518,7 @@ static int8_t SCSI_Read10(USBD_HandleTypeDef  *pdev, uint8_t lun , uint8_t *para
     }
 
     hmsc->bot_state = USBD_BOT_DATA_IN;
-    hmsc->scsi_blk_len  *= hmsc->scsi_blk_size;
+    hmsc->scsi_blk_len *= hmsc->scsi_blk_size[lun];
 
     /* cases 4,5 : Hi <> Dn */
     if (hmsc->cbw.dDataLength != hmsc->scsi_blk_len)
@@ -596,7 +598,7 @@ static int8_t SCSI_Write10 (USBD_HandleTypeDef  *pdev, uint8_t lun , uint8_t *pa
       return -1; /* error */
     }
 
-    hmsc->scsi_blk_len  *= hmsc->scsi_blk_size;
+    hmsc->scsi_blk_len *= hmsc->scsi_blk_size[lun];
 
     /* cases 3,11,13 : Hn,Ho <> D0 */
     if (hmsc->cbw.dDataLength != hmsc->scsi_blk_len)
@@ -670,7 +672,7 @@ static int8_t SCSI_CheckAddressRange (USBD_HandleTypeDef  *pdev, uint8_t lun , u
 {
   USBD_MSC_BOT_HandleTypeDef *hmsc = &((usbd_cdc_msc_hid_state_t*)pdev->pClassData)->MSC_BOT_ClassData;
 
-  if ((blk_offset + blk_nbr) > hmsc->scsi_blk_nbr )
+  if ((blk_offset + blk_nbr) > hmsc->scsi_blk_nbr[lun])
   {
     SCSI_SenseCode(pdev,
                    lun,
@@ -697,7 +699,7 @@ static int8_t SCSI_ProcessRead (USBD_HandleTypeDef  *pdev, uint8_t lun)
   if( hmsc->bdev_ops->Read(lun ,
                               hmsc->bot_data,
                               hmsc->scsi_blk_addr_in_blks,
-                              len / hmsc->scsi_blk_size) < 0)
+                              len / hmsc->scsi_blk_size[lun]) < 0)
   {
 
     SCSI_SenseCode(pdev,
@@ -714,7 +716,7 @@ static int8_t SCSI_ProcessRead (USBD_HandleTypeDef  *pdev, uint8_t lun)
              len);
 
 
-  hmsc->scsi_blk_addr_in_blks += len / hmsc->scsi_blk_size;
+  hmsc->scsi_blk_addr_in_blks += len / hmsc->scsi_blk_size[lun];
   hmsc->scsi_blk_len    -= len;
 
   /* case 6 : Hi = Di */
@@ -744,7 +746,7 @@ static int8_t SCSI_ProcessWrite (USBD_HandleTypeDef  *pdev, uint8_t lun)
   if(hmsc->bdev_ops->Write(lun ,
                               hmsc->bot_data,
                               hmsc->scsi_blk_addr_in_blks,
-                              len / hmsc->scsi_blk_size) < 0)
+                              len / hmsc->scsi_blk_size[lun]) < 0)
   {
     SCSI_SenseCode(pdev,
                    lun,
@@ -754,7 +756,7 @@ static int8_t SCSI_ProcessWrite (USBD_HandleTypeDef  *pdev, uint8_t lun)
   }
 
 
-  hmsc->scsi_blk_addr_in_blks += len / hmsc->scsi_blk_size;
+  hmsc->scsi_blk_addr_in_blks += len / hmsc->scsi_blk_size[lun];
   hmsc->scsi_blk_len   -= len;
 
   /* case 12 : Ho = Do */