diff --git a/libsrc/atari/is_cmdline_dos.s b/libsrc/atari/is_cmdline_dos.s
new file mode 100644
index 000000000..71b35fbad
--- /dev/null
+++ b/libsrc/atari/is_cmdline_dos.s
@@ -0,0 +1,20 @@
+;
+; Christian Groessler, May-2016
+;
+; unsigned char _is_cmdline_dos(void);
+;
+; returns 0 for non-commandline DOS, 1 for commandline DOS
+;
+
+        .export  __is_cmdline_dos
+        .import  __dos_type
+        .include "atari.inc"
+
+__is_cmdline_dos:
+        ldx     #0
+        lda     __dos_type
+        cmp     #MAX_DOS_WITH_CMDLINE + 1
+        txa
+        rol     a
+        eor     #$01
+        rts