diff --git a/backend/mustek_usb2_asic.c b/backend/mustek_usb2_asic.c
index 0af3607d0..2eb1057a2 100644
--- a/backend/mustek_usb2_asic.c
+++ b/backend/mustek_usb2_asic.c
@@ -1627,7 +1627,6 @@ SetPackAddress (ASIC * chip, unsigned short wWidth, unsigned short wX,
   SendData (chip, ES01_CE_TG_G_CONTROL, 0);
   SendData (chip, ES01_CF_TG_B_CONTROL, 0x3C);
 
-
   /* set pack area address */
   SendData (chip, ES01_16D_EXPOSURE_CYCLE1_SEGMENT1_START_ADDR_BYTE0,
 	    BYTE0 (PACK_AREA_START_ADDRESS));
@@ -1649,7 +1648,6 @@ SetPackAddress (ASIC * chip, unsigned short wWidth, unsigned short wX,
     SendData (chip, 0x260 + i, 0);
   DBG (DBG_ASIC, "set invalid pixel finished\n");
 
-
   /* set pack start address */
   SendData (chip, ES01_19E_PACK_AREA_R_START_ADDR_BYTE0,
 	    BYTE0 (PACK_AREA_START_ADDRESS));
@@ -1944,7 +1942,6 @@ Asic_TurnLamp (ASIC * chip, SANE_Bool isLampOn)
   return SANE_STATUS_GOOD;
 }
 
-
 SANE_Status
 Asic_TurnTA (ASIC * chip, SANE_Bool isTAOn)
 {
diff --git a/backend/mustek_usb2_high.c b/backend/mustek_usb2_high.c
index ef13fbbd6..6f4d9f947 100644
--- a/backend/mustek_usb2_high.c
+++ b/backend/mustek_usb2_high.c
@@ -806,6 +806,8 @@ ReadDataFromScanner (void * param)
 	  DBG (DBG_FUNC, "ReadDataFromScanner: wScanLinesThisBlock=%d\n",
 	       wScanLinesThisBlock);
 
+	  /* This call is thread-safe under the assumption that no function that
+	     might run concurrently will cause a register bank switch. */
 	  if (Asic_ReadImage (&st->chip, pReadImage, wScanLinesThisBlock) !=
 	      SANE_STATUS_GOOD)
 	    {
@@ -826,9 +828,8 @@ ReadDataFromScanner (void * param)
 	      wReadImageLines = 0;
 	    }
 
-	  if ((st->dwScannedTotalLines - GetReadyLines (st)) >=
-	      (wMaxScanLines - (wBufferLines + st->wScanLinesPerBlock)) &&
-	      st->dwScannedTotalLines > GetReadyLines (st))
+	  if (st->dwScannedTotalLines >= (GetReadyLines (st) +
+	      (wMaxScanLines - (wBufferLines + st->wScanLinesPerBlock))))
 	    {
 	      isWaitImageLineDiff = SANE_TRUE;
 	    }