diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index e20a2f6..733a7b9 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -176,7 +176,7 @@
  * The main open() function
  */
 PyDoc_STRVAR(open_doc,
-"open(file, mode='r', buffering=None, encoding=None,\n"
+"open(file, mode='r', buffering=-1, encoding=None,\n"
 "     errors=None, newline=None, closefd=True) -> file object\n"
 "\n"
 "Open file and return a stream.  Raise IOError upon failure.\n"