diff --git a/include/mmc.h b/include/mmc.h
index 7e026da..3594286 100644
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -187,6 +187,9 @@
 #define EXT_CSD_BOOT_PART_NUM(x)	(x << 3)
 #define EXT_CSD_PARTITION_ACCESS(x)	(x << 0)
 
+#define EXT_CSD_BOOT_BUS_WIDTH_MODE(x)	(x << 3)
+#define EXT_CSD_BOOT_BUS_WIDTH_RESET(x)	(x << 2)
+#define EXT_CSD_BOOT_BUS_WIDTH_WIDTH(x)	(x)
 
 #define R1_ILLEGAL_COMMAND		(1 << 22)
 #define R1_APP_CMD			(1 << 5)
@@ -314,6 +317,8 @@
 int mmc_boot_part_access(struct mmc *mmc, u8 ack, u8 part_num, u8 access);
 /* Function to modify the PARTITION_CONFIG field of EXT_CSD */
 int mmc_set_part_conf(struct mmc *mmc, u8 ack, u8 part_num, u8 access);
+/* Function to modify the BOOT_BUS_WIDTH field of EXT_CSD */
+int mmc_set_boot_bus_width(struct mmc *mmc, u8 width, u8 reset, u8 mode);
 
 /**
  * Start device initialization and return immediately; it does not block on