diff --git a/sys/dev/mmc/host/dwmmc.c b/sys/dev/mmc/host/dwmmc.c
--- a/sys/dev/mmc/host/dwmmc.c
+++ b/sys/dev/mmc/host/dwmmc.c
@@ -1354,8 +1354,8 @@
 		 * (on start and on end) for bounced fragments.
 		 *
 		 */
-		*(int *)result = (IDMAC_MAX_SIZE * IDMAC_DESC_SEGS) /
-		    MMC_SECTOR_SIZE - 3;
+		*(int *)result = (IDMAC_MAX_SIZE * (IDMAC_DESC_SEGS - 2)) /
+		    MMC_SECTOR_SIZE ;
 		break;
 	case MMCBR_IVAR_TIMING:
 		*(int *)result = sc->host.ios.timing;