diff --git a/libsrc/c1p/oserror.s b/libsrc/c1p/oserror.s
new file mode 100644
index 000000000..073691a06
--- /dev/null
+++ b/libsrc/c1p/oserror.s
@@ -0,0 +1,20 @@
+;
+; dummy implementation for Challenger 1P based on atmos implementation
+;
+; original by
+; Stefan Haubenthal, 2011-04-18
+;
+; int __fastcall__ _osmaperrno (unsigned char oserror);
+; /* Map a system specific error into a system independent code */
+;
+
+        .include        "errno.inc"
+        .export         __osmaperrno
+
+.proc   __osmaperrno
+
+        lda     #<EUNKNOWN
+        ldx     #>EUNKNOWN
+        rts
+
+.endproc