diff --git a/stmhal/usbd_msc_storage.c b/stmhal/usbd_msc_storage.c
index ab2d4459ab..c0e4468362 100644
--- a/stmhal/usbd_msc_storage.c
+++ b/stmhal/usbd_msc_storage.c
@@ -41,10 +41,10 @@
 
 // These are needed to support removal of the medium, so that the USB drive
 // can be unmounted, and won't be remounted automatically.
-static uint8_t flash_removed = 0;
+static uint8_t flash_started = 0;
 
 #if MICROPY_HW_HAS_SDCARD
-static uint8_t sdcard_removed = 0;
+static uint8_t sdcard_started = 0;
 #endif
 
 /******************************************************************************/
@@ -73,6 +73,7 @@ static const int8_t FLASH_STORAGE_Inquirydata[] = { // 36 bytes
   */
 int8_t FLASH_STORAGE_Init(uint8_t lun) {
     storage_init();
+    flash_started = 1;
     return 0;
 }
 
@@ -95,10 +96,10 @@ int8_t FLASH_STORAGE_GetCapacity(uint8_t lun, uint32_t *block_num, uint16_t *blo
   * @retval Status
   */
 int8_t FLASH_STORAGE_IsReady(uint8_t lun) {
-    if (flash_removed) {
-        return -1;
+    if (flash_started) {
+        return 0;
     }
-    return 0;
+    return -1;
 }
 
 /**
@@ -111,8 +112,8 @@ int8_t FLASH_STORAGE_IsWriteProtected(uint8_t lun) {
 }
 
 // Remove the lun
-int8_t FLASH_STORAGE_StopUnit(uint8_t lun) {
-    flash_removed = 1;
+int8_t FLASH_STORAGE_StartStopUnit(uint8_t lun, uint8_t started) {
+    flash_started = started;
     return 0;
 }
 
@@ -176,7 +177,7 @@ const USBD_StorageTypeDef USBD_FLASH_STORAGE_fops = {
     FLASH_STORAGE_GetCapacity,
     FLASH_STORAGE_IsReady,
     FLASH_STORAGE_IsWriteProtected,
-    FLASH_STORAGE_StopUnit,
+    FLASH_STORAGE_StartStopUnit,
     FLASH_STORAGE_PreventAllowMediumRemoval,
     FLASH_STORAGE_Read,
     FLASH_STORAGE_Write,
@@ -228,7 +229,7 @@ int8_t SDCARD_STORAGE_Init(uint8_t lun) {
     if (!sdcard_power_on()) {
         return -1;
     }
-
+    sdcard_started = 1;
     return 0;
 
 }
@@ -264,33 +265,10 @@ int8_t SDCARD_STORAGE_GetCapacity(uint8_t lun, uint32_t *block_num, uint16_t *bl
   * @retval Status
   */
 int8_t SDCARD_STORAGE_IsReady(uint8_t lun) {
-    if (sdcard_removed) {
-        return -1;
+    if (sdcard_started) {
+        return 0;
     }
-    /*
-#ifndef USE_STM3210C_EVAL  
-  
-  static int8_t last_status = 0;
-
-  if(last_status  < 0)
-  {
-    SD_Init();
-    last_status = 0;
-  }
-  
-  if(SD_GetStatus() != 0)
-  {
-    last_status = -1;
-    return (-1); 
-  }  
-#else
-  if( SD_Init() != 0)
-  {
-    return (-1);
-  }  
-#endif
-*/
-    return 0;
+    return -1;
 }
 
 /**
@@ -303,8 +281,8 @@ int8_t SDCARD_STORAGE_IsWriteProtected(uint8_t lun) {
 }
 
 // Remove the lun
-int8_t SDCARD_STORAGE_StopUnit(uint8_t lun) {
-    sdcard_removed = 1;
+int8_t SDCARD_STORAGE_StartStopUnit(uint8_t lun, uint8_t started) {
+    sdcard_started = started;
     return 0;
 }
 
@@ -356,7 +334,7 @@ const USBD_StorageTypeDef USBD_SDCARD_STORAGE_fops = {
     SDCARD_STORAGE_GetCapacity,
     SDCARD_STORAGE_IsReady,
     SDCARD_STORAGE_IsWriteProtected,
-    SDCARD_STORAGE_StopUnit,
+    SDCARD_STORAGE_StartStopUnit,
     SDCARD_STORAGE_PreventAllowMediumRemoval,
     SDCARD_STORAGE_Read,
     SDCARD_STORAGE_Write,
diff --git a/stmhal/usbdev/class/cdc_msc_hid/inc/usbd_cdc_msc_hid.h b/stmhal/usbdev/class/cdc_msc_hid/inc/usbd_cdc_msc_hid.h
index 7eca900ee0..48d260bc25 100644
--- a/stmhal/usbdev/class/cdc_msc_hid/inc/usbd_cdc_msc_hid.h
+++ b/stmhal/usbdev/class/cdc_msc_hid/inc/usbd_cdc_msc_hid.h
@@ -58,7 +58,7 @@ typedef struct _USBD_STORAGE {
   int8_t (* GetCapacity) (uint8_t lun, uint32_t *block_num, uint16_t *block_size);
   int8_t (* IsReady) (uint8_t lun);
   int8_t (* IsWriteProtected) (uint8_t lun);
-  int8_t (* StopUnit)(uint8_t lun);
+  int8_t (* StartStopUnit)(uint8_t lun, uint8_t started);
   int8_t (* PreventAllowMediumRemoval)(uint8_t lun, uint8_t param0);
   int8_t (* Read) (uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len);
   int8_t (* Write)(uint8_t lun, uint8_t *buf, uint32_t blk_addr, uint16_t blk_len);
diff --git a/stmhal/usbdev/class/cdc_msc_hid/src/usbd_msc_scsi.c b/stmhal/usbdev/class/cdc_msc_hid/src/usbd_msc_scsi.c
index 894812c18f..366f1f00e9 100644
--- a/stmhal/usbdev/class/cdc_msc_hid/src/usbd_msc_scsi.c
+++ b/stmhal/usbdev/class/cdc_msc_hid/src/usbd_msc_scsi.c
@@ -450,13 +450,10 @@ static int8_t SCSI_StartStopUnit(USBD_HandleTypeDef  *pdev, uint8_t lun, uint8_t
   hmsc->bot_data_length = 0;
 
   // On Mac OS X, when the device is ejected a SCSI_START_STOP_UNIT command is sent.
-  // params[1]==0 means stop, param[1]==1 seems to be something else (happens after the
-  // device is plugged in and mounted for some time, probably a keep alive).
+  // Bit 0 of params[4] is the START bit.
   // If we get a stop, we must really stop the device so that the Mac does not
   // automatically remount it.
-  if (params[1] == 0) {
-      ((USBD_StorageTypeDef *)pdev->pUserData)->StopUnit(lun);
-  }
+  ((USBD_StorageTypeDef *)pdev->pUserData)->StartStopUnit(lun, params[4] & 1);
 
   return 0;
 }