diff --git a/asminc/errno.inc b/asminc/errno.inc
index 96b5bf94e..ef81036fc 100644
--- a/asminc/errno.inc
+++ b/asminc/errno.inc
@@ -7,6 +7,7 @@
         .global         __errno, __oserror
         .global         __maperrno, __osmaperrno
         .global         __seterrno
+        .global         oserrcheck, setoserror
 
 ; Error codes, must match the values in the C headers
 .enum
diff --git a/libsrc/common/maperrno.s b/libsrc/common/maperrno.s
index 528888e7b..869acac6f 100644
--- a/libsrc/common/maperrno.s
+++ b/libsrc/common/maperrno.s
@@ -4,6 +4,9 @@
 ; void _maperrno(void);
 ; /* Map an OS error to a system independent error code */
 ;
+; Second entry setoserror maps the OS error code in A to an errno code
+; and stores it into errno. _oserror is cleared.
+
 
         .include        "errno.inc"
 
@@ -13,6 +16,7 @@
 __maperrno:
 	lda	__oserror		; Get the error code
 	beq	@L1			; Jump if no error
+setoserror:       
 	ldx	#$00			; Clear error
 	stx	__oserror
 	jsr	__osmaperrno		; Map the code