diff --git a/libc/kernel/uapi/linux/serial.h b/libc/kernel/uapi/linux/serial.h
index adbdd1b..ed5ed66 100644
--- a/libc/kernel/uapi/linux/serial.h
+++ b/libc/kernel/uapi/linux/serial.h
@@ -6,6 +6,7 @@
  */
 #ifndef _UAPI_LINUX_SERIAL_H
 #define _UAPI_LINUX_SERIAL_H
+#include <linux/const.h>
 #include <linux/types.h>
 #include <linux/tty_flags.h>
 struct serial_struct {
@@ -79,14 +80,15 @@
 };
 struct serial_rs485 {
   __u32 flags;
-#define SER_RS485_ENABLED (1 << 0)
-#define SER_RS485_RTS_ON_SEND (1 << 1)
-#define SER_RS485_RTS_AFTER_SEND (1 << 2)
-#define SER_RS485_RX_DURING_TX (1 << 4)
-#define SER_RS485_TERMINATE_BUS (1 << 5)
-#define SER_RS485_ADDRB (1 << 6)
-#define SER_RS485_ADDR_RECV (1 << 7)
-#define SER_RS485_ADDR_DEST (1 << 8)
+#define SER_RS485_ENABLED _BITUL(0)
+#define SER_RS485_RTS_ON_SEND _BITUL(1)
+#define SER_RS485_RTS_AFTER_SEND _BITUL(2)
+#define SER_RS485_RX_DURING_TX _BITUL(4)
+#define SER_RS485_TERMINATE_BUS _BITUL(5)
+#define SER_RS485_ADDRB _BITUL(6)
+#define SER_RS485_ADDR_RECV _BITUL(7)
+#define SER_RS485_ADDR_DEST _BITUL(8)
+#define SER_RS485_MODE_RS422 _BITUL(9)
   __u32 delay_rts_before_send;
   __u32 delay_rts_after_send;
   union {