diff --git a/Source/HBIOS/Config/RCZ280_nat.asm b/Source/HBIOS/Config/RCZ280_nat.asm
index a1b105d2..b80be899 100644
--- a/Source/HBIOS/Config/RCZ280_nat.asm
+++ b/Source/HBIOS/Config/RCZ280_nat.asm
@@ -40,7 +40,7 @@ Z280_INTWAIT	.SET	0		; Z280: INT ACK WAIT STATUS (0-3)
 ;
 Z2UENABLE	.SET	TRUE		; Z2U: ENABLE Z280 UART SERIAL DRIVER (Z2U.ASM)
 UARTENABLE	.SET	TRUE		; UART: ENABLE 8250/16550-LIKE SERIAL DRIVER (UART.ASM)
-ACIAENABLE	.SET	FALSE		; ACIA: ENABLE MOTOROLA 6850 ACIA DRIVER (ACIA.ASM)
+ACIAENABLE	.SET	TRUE		; ACIA: ENABLE MOTOROLA 6850 ACIA DRIVER (ACIA.ASM)
 SIOENABLE	.SET	TRUE		; SIO: ENABLE ZILOG SIO SERIAL DRIVER (SIO.ASM)
 ;
 IDEENABLE	.SET	TRUE		; IDE: ENABLE IDE DISK DRIVER (IDE.ASM)
diff --git a/Source/HBIOS/acia.asm b/Source/HBIOS/acia.asm
index 1ca7f218..54832171 100644
--- a/Source/HBIOS/acia.asm
+++ b/Source/HBIOS/acia.asm
@@ -57,11 +57,6 @@ ACIA_ACIA       .EQU    1
 ACIA_RTSON	.EQU	%00000000	; BIT MASK TO ASSERT RTS
 ACIA_RTSOFF	.EQU	%01000000	; BIT MASK TO DEASSERT RTS
 ;
-#IF (INTMODE > 1)
-        .ECHO   "*** ERROR: UNSUPPORTED INTMODE FOR ACIA DRIVER!!!\n"
-        !!!     ; FORCE AN ASSEMBLY ERROR
-#ENDIF
-;
 ;
 ;
 ACIA_PREINIT:
@@ -119,11 +114,6 @@ ACIA_INITUNIT:
         LD      H,(IY+9)		; ... INTO HL
         CALL    HB_ADDIM1               ; ADD TO IM1 CALL LIST
 #ENDIF
-;
-#IF (INTMODE > 1)
-	.ECHO	"*** ERROR: ACIA DEVICE DOES NOT SUPPORT INTMODE 2!!!\n"
-	!!!	; FORCE AN ASSEMBLY ERROR
-#ENDIF
 ;
 	; IT IS EASY TO SPECIFY A SERIAL CONFIG THAT CANNOT BE IMPLEMENTED
 	; DUE TO THE CONSTRAINTS OF THE ACIA.  HERE WE FORCE A GENERIC
@@ -158,7 +148,7 @@ ACIA_INIT1:
 ;
 ; INTERRUPT HANDLERS
 ;
-#IF (INTMODE == 0)
+#IF (INTMODE != 1)
 ;
 ; NO INTERRUPT HANDLERS UNDER INTMODE 0.  GENERATE A PANIC
 ; IF SOMETHING TRIES TO CALL THEM.
@@ -169,7 +159,7 @@ ACIA1_INT:
 ;
 #ENDIF
 ;
-#IF (INTMODE > 0)
+#IF (INTMODE == 1)
 ;
 ACIA0_INT:
 	LD	IY,ACIA0_CFG		; POINT TO ACIA0 CFG
@@ -263,7 +253,7 @@ ACIA_FNTBL:
 ;
 ;
 ;
-#IF (INTMODE == 0)
+#IF (INTMODE != 1)
 ;
 ACIA_IN:
         CALL    ACIA_IST                ; CHAR WAITING?
@@ -336,7 +326,7 @@ ACIA_OUT:
 ;
 ;
 ;
-#IF (INTMODE == 0)
+#IF (INTMODE != 1)
 ;
 ACIA_IST:
         LD      C,(IY+3)                ; STATUS PORT
@@ -510,7 +500,7 @@ ACIA_INITSAFE:
 ;
 ACIA_INITGO:
 ;
-#IF (INTMODE > 0)
+#IF (INTMODE == 1)
 	OR	%10000000		; ENABLE RCV INT
 #ENDIF
 ;
@@ -530,7 +520,7 @@ ACIA_INITGO:
 	LD	A,(ACIA_CMD)		; RESTORE CONFIG VALUE
         OUT     (C),A                   ; DO IT
 ;
-#IF (INTMODE > 0)
+#IF (INTMODE == 1)
 ;
         ; RESET THE RECEIVE BUFFER
         LD      E,(IY+6)
@@ -657,7 +647,7 @@ ACIA_STR_ACIA   .DB     "ACIA$"
 ACIA_DEV        .DB     0               ; DEVICE NUM USED DURING INIT
 ACIA_CMD	.DB	0		; COMMAND PORT SHADOW REGISTER
 ;
-#IF (INTMODE == 0)
+#IF (INTMODE != 1)
 ;
 ACIA0_RCVBUF    .EQU    0
 ACIA1_RCVBUF    .EQU    0
diff --git a/Source/ver.inc b/Source/ver.inc
index 49dabc01..289c3d7e 100644
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,4 +2,4 @@
 #DEFINE	RMN	1
 #DEFINE	RUP	1
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.1.1-pre.38"
+#DEFINE BIOSVER	"3.1.1-pre.39"
diff --git a/Source/ver.lib b/Source/ver.lib
index 973c277f..37751c05 100644
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	1
 rup	equ	1
 rtp	equ	0
 biosver	macro
-	db	"3.1.1-pre.38"
+	db	"3.1.1-pre.39"
 	endm