Check for correct macro, code uses S_ISDIR().
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index ff7d14d..34a5801 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -171,7 +171,7 @@
 static int
 dircheck(fileio* self, PyObject *nameobj)
 {
-#if defined(HAVE_FSTAT) && defined(S_IFDIR) && defined(EISDIR)
+#if defined(HAVE_FSTAT) && defined(S_ISDIR) && defined(EISDIR)
     struct stat buf;
     if (self->fd < 0)
         return 0;