diff --git a/cmd/fastboot/Kconfig b/cmd/fastboot/Kconfig
index 7330da2..214bbc2 100644
--- a/cmd/fastboot/Kconfig
+++ b/cmd/fastboot/Kconfig
@@ -74,6 +74,8 @@
 config FASTBOOT_FLASH_MMC_DEV
 	int "Define FASTBOOT MMC FLASH default device"
 	depends on FASTBOOT_FLASH && MMC
+	default 0 if ARCH_SUNXI && MMC_SUNXI_SLOT_EXTRA = -1
+	default 1 if ARCH_SUNXI && MMC_SUNXI_SLOT_EXTRA != -1
 	help
 	  The fastboot "flash" command requires additional information
 	  regarding the non-volatile storage device. Define this to