diff --git a/libsrc/atari/is_cmdline_dos.s b/libsrc/atari/is_cmdline_dos.s
index eb474dbfb..2a9c49e38 100644
--- a/libsrc/atari/is_cmdline_dos.s
+++ b/libsrc/atari/is_cmdline_dos.s
@@ -11,9 +11,8 @@
         .include "atari.inc"
 
 __is_cmdline_dos:
-        lda     __dos_type
-        cmp     #MAX_DOS_WITH_CMDLINE + 1
+        lda     #MAX_DOS_WITH_CMDLINE
+        cmp     __dos_type
         lda     #0
         rol     a
-        eor     #$01
         rts