diff --git a/Source/HBIOS/plt_rc180.inc b/Source/HBIOS/plt_rc180.inc
index 2ab74f51..950801b1 100644
--- a/Source/HBIOS/plt_rc180.inc
+++ b/Source/HBIOS/plt_rc180.inc
@@ -11,7 +11,6 @@ MPGENA		.EQU	SBC_BASE + $1C	; PAGING ENABLE REGISTER - BIT 0 = 1  (WRITE ONLY)
 ;
 RTC		.EQU	SBC_BASE + $10	; ADDRESS OF RTC LATCH AND INPUT PORT
 PPIBASE		.EQU	SBC_BASE + $00	; PPI 82C55 I/O IS DECODED TO PORT 60-67
-SIOBASE		.EQU	SBC_BASE + $08	; 16550 UART I/O BASE ADDRESS
 ;
 Z180_BASE	.EQU	$C0		; I/O BASE ADDRESS FOR INTERNAL Z180 REGISTERS
 #INCLUDE "z180.inc"
diff --git a/Source/HBIOS/plt_sbc.inc b/Source/HBIOS/plt_sbc.inc
index d500249b..e74806a2 100644
--- a/Source/HBIOS/plt_sbc.inc
+++ b/Source/HBIOS/plt_sbc.inc
@@ -19,4 +19,3 @@ MPGENA		.EQU	SBC_BASE + $1C	; PAGING ENABLE REGISTER - BIT 0 = 1  (WRITE ONLY)
 ;
 RTC		.EQU	SBC_BASE + $10	; ADDRESS OF RTC LATCH AND INPUT PORT
 PPIBASE		.EQU	SBC_BASE + $00	; PPI 82C55 I/O IS DECODED TO PORT 60-67
-SIOBASE		.EQU	SBC_BASE + $08	; 16550 UART I/O BASE ADDRESS