diff --git a/arch/mn10300/unit-asb2364/include/unit/serial.h b/arch/mn10300/unit-asb2364/include/unit/serial.h
index 7f048bbfdfd7f0edc8833261ca751a4a5b17f85e..92f224a97efcc612ba8fa2610d335d04e9cd788c 100644
--- a/arch/mn10300/unit-asb2364/include/unit/serial.h
+++ b/arch/mn10300/unit-asb2364/include/unit/serial.h
@@ -59,18 +59,18 @@ static inline void __debug_to_serial(const char *p, int n)
 #define SERIAL_PORT_DFNS /* stolen by gdb-stub */
 
 #if defined(CONFIG_GDBSTUB_ON_TTYS0)
-#define GDBPORT_SERIAL_RX	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_RX  * 4, u8)
-#define GDBPORT_SERIAL_TX	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_TX  * 4, u8)
-#define GDBPORT_SERIAL_DLL	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_DLL * 4, u8)
-#define GDBPORT_SERIAL_DLM	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_DLM * 4, u8)
-#define GDBPORT_SERIAL_IER	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_IER * 4, u8)
-#define GDBPORT_SERIAL_IIR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_IIR * 4, u8)
-#define GDBPORT_SERIAL_FCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_FCR * 4, u8)
-#define GDBPORT_SERIAL_LCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_LCR * 4, u8)
-#define GDBPORT_SERIAL_MCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_MCR * 4, u8)
-#define GDBPORT_SERIAL_LSR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_LSR * 4, u8)
-#define GDBPORT_SERIAL_MSR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_MSR * 4, u8)
-#define GDBPORT_SERIAL_SCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_SCR * 4, u8)
+#define GDBPORT_SERIAL_RX	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_RX  * 2, u8)
+#define GDBPORT_SERIAL_TX	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_TX  * 2, u8)
+#define GDBPORT_SERIAL_DLL	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_DLL * 2, u8)
+#define GDBPORT_SERIAL_DLM	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_DLM * 2, u8)
+#define GDBPORT_SERIAL_IER	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_IER * 2, u8)
+#define GDBPORT_SERIAL_IIR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_IIR * 2, u8)
+#define GDBPORT_SERIAL_FCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_FCR * 2, u8)
+#define GDBPORT_SERIAL_LCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_LCR * 2, u8)
+#define GDBPORT_SERIAL_MCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_MCR * 2, u8)
+#define GDBPORT_SERIAL_LSR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_LSR * 2, u8)
+#define GDBPORT_SERIAL_MSR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_MSR * 2, u8)
+#define GDBPORT_SERIAL_SCR	__SYSREG(SERIAL_PORT0_BASE_ADDRESS + UART_SCR * 2, u8)
 #define GDBPORT_SERIAL_IRQ	SERIAL_IRQ
 
 #elif defined(CONFIG_GDBSTUB_ON_TTYS1)