diff --git a/sys/dev/iicbus/iic.h b/sys/dev/iicbus/iic.h
--- a/sys/dev/iicbus/iic.h
+++ b/sys/dev/iicbus/iic.h
@@ -40,6 +40,7 @@
 #define	IIC_M_RD	0x0001	/* read vs write */
 #define	IIC_M_NOSTOP	0x0002	/* do not send a I2C stop after message */
 #define	IIC_M_NOSTART	0x0004	/* do not send a I2C start before message */
+#define	IIC_M_CMD	0x0008	/* command and/or offset for read/write */
 	uint16_t	len;	/* msg length */
 	uint8_t *	buf;
 };