diff --git a/cc65-dio-fix/dioopen.s b/cc65-dio-fix/dioopen.s
new file mode 100644
index 0000000..3146a74
--- /dev/null
+++ b/cc65-dio-fix/dioopen.s
@@ -0,0 +1,52 @@
+;
+; Oliver Schmidt, 24.03.2005
+;
+; dhandle_t __fastcall__ dio_open (unsigned char device);
+;
+
+        .export         _dio_open
+        .import         return0, __dos_type, isdevice
+
+        .include        "errno.inc"
+        .include        "mli.inc"
+        .include        "zeropage.inc"
+
+_dio_open:
+        ; Check for ProDOS 8
+        ldx     __dos_type
+        bne     :+
+        lda     #$01            ; "Bad system call number"
+        bne     oserr           ; Branch always
+
+        ; Convert from 00DDDSSS format to DSSS00DD format
+:		tax
+        clc
+        asl
+        asl
+        asl
+        asl
+        sta     tmp1
+        txa
+        lsr
+        lsr
+        lsr
+        lsr
+        ora     tmp1
+
+        ; Check for valid device
+        tax
+
+        jsr     isdevice
+        beq     :+
+        lda     #$28            ; "No device connected"
+
+        ; Return oserror
+oserr:  sta     __oserror
+        jmp     return0
+
+        ; Return success
+:       txa
+
+        ldx     #$00
+        stx     __oserror
+        rts
diff --git a/cc65-dio-fix/isdevice.s b/cc65-dio-fix/isdevice.s
new file mode 100644
index 0000000..97c7a83
--- /dev/null
+++ b/cc65-dio-fix/isdevice.s
@@ -0,0 +1,18 @@
+;
+; Oliver Schmidt, 2012-10-15
+;
+
+        .export         isdevice
+
+        .include        "zeropage.inc"
+        .include        "mli.inc"
+
+isdevice:
+        ldy     DEVCNT
+:       lda     DEVLST,y
+        sta     tmp1
+        cpx     tmp1
+        beq     :+
+        dey
+        bpl     :-
+:       rts