diff --git a/src/port.c b/src/port.c
index e569ca3d..ebcd6dbb 100644
--- a/src/port.c
+++ b/src/port.c
@@ -82,12 +82,19 @@ pic_funopen(void *cookie,
   if (! file) {
     return NULL;
   }
+  /* no buffering at the beginning */
+  file->buf = NULL;
+  file->mode = _IONBF;
+  file->bufsiz = 0;
+  /* set vtable */
   file->vtable.cookie = cookie;
   file->vtable.read = read;
   file->vtable.write = write;
   file->vtable.seek = seek;
   file->vtable.close = close;
 
+  pic_setvbuf(file, (char *)NULL, _IOFBF, 0);
+
   return file;
 }