diff --git a/sys/dev/sio/sioreg.h b/sys/dev/sio/sioreg.h
index e0ba5ad5b13..028f8326375 100644
--- a/sys/dev/sio/sioreg.h
+++ b/sys/dev/sio/sioreg.h
@@ -107,6 +107,7 @@
 
 #ifdef PC98
 /* Hardware extension mode register for RSB-2000/3000. */
+#define	com_emr		com_msr
 #define	EMR_EXBUFF	0x04
 #define	EMR_CTSFLW	0x08
 #define	EMR_DSRFLW	0x10
diff --git a/sys/pc98/cbus/sio.c b/sys/pc98/cbus/sio.c
index 7643b8d25c6..6d8c7d6ecfc 100644
--- a/sys/pc98/cbus/sio.c
+++ b/sys/pc98/cbus/sio.c
@@ -190,10 +190,6 @@
 #define COM_IIR_TXRDYBUG(flags)	((flags) & COM_C_IIR_TXRDYBUG)
 #define	COM_FIFOSIZE(flags)	(((flags) & 0xff000000) >> 24)
 
-#ifdef PC98
-#define	com_emr		com_msr	/* Extension mode register for RSB-2000/3000 */
-#endif
-
 #define	sio_getreg(com, off) \
 	(bus_space_read_1((com)->bst, (com)->bsh, (off)))
 #define	sio_setreg(com, off, value) \
diff --git a/sys/pc98/pc98/sio.c b/sys/pc98/pc98/sio.c
index 7643b8d25c6..6d8c7d6ecfc 100644
--- a/sys/pc98/pc98/sio.c
+++ b/sys/pc98/pc98/sio.c
@@ -190,10 +190,6 @@
 #define COM_IIR_TXRDYBUG(flags)	((flags) & COM_C_IIR_TXRDYBUG)
 #define	COM_FIFOSIZE(flags)	(((flags) & 0xff000000) >> 24)
 
-#ifdef PC98
-#define	com_emr		com_msr	/* Extension mode register for RSB-2000/3000 */
-#endif
-
 #define	sio_getreg(com, off) \
 	(bus_space_read_1((com)->bst, (com)->bsh, (off)))
 #define	sio_setreg(com, off, value) \