diff --git a/reactos/include/crt/errno.h b/reactos/include/crt/errno.h
index 944b3ad504b..8e8917b5458 100644
--- a/reactos/include/crt/errno.h
+++ b/reactos/include/crt/errno.h
@@ -17,8 +17,8 @@ extern "C" {
   _CRTIMP extern int *__cdecl _errno(void);
 #define errno (*_errno())
 
-  errno_t __cdecl _set_errno(int _Value);
-  errno_t __cdecl _get_errno(int *_Value);
+  errno_t __cdecl _set_errno(_In_ int _Value);
+  errno_t __cdecl _get_errno(_Out_ int *_Value);
 #endif
 
 #define EPERM 1