diff --git a/libsrc/atmos/oserror.s b/libsrc/atmos/oserror.s
index befbdffbf..aa54ea585 100644
--- a/libsrc/atmos/oserror.s
+++ b/libsrc/atmos/oserror.s
@@ -1,11 +1,17 @@
 ;
-; Stefan Haubenthal, 2011-04-10
+; 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
-	.import		return0
 
-__osmaperrno	= return0
+.proc	__osmaperrno
+
+	lda	#<EUNKNOWN
+	ldx	#>EUNKNOWN
+	rts
+
+.endproc