diff -r 1c5e0dbcb2a0 Doc/library/os.rst
--- a/Doc/library/os.rst	Sun Sep 25 16:54:17 2016 +0300
+++ b/Doc/library/os.rst	Sun Sep 25 18:41:08 2016 +0200
@@ -3506,7 +3506,7 @@
    .. versionadded:: 3.3
 
 
-.. function:: waitpid(pid, options)
+.. function:: waitpid(pid, options=0)
 
    The details of this function differ on Unix and Windows.
 
diff -r 1c5e0dbcb2a0 Modules/clinic/posixmodule.c.h
--- a/Modules/clinic/posixmodule.c.h	Sun Sep 25 16:54:17 2016 +0300
+++ b/Modules/clinic/posixmodule.c.h	Sun Sep 25 18:41:08 2016 +0200
@@ -2963,7 +2963,7 @@
 #if defined(HAVE_WAITPID)
 
 PyDoc_STRVAR(os_waitpid__doc__,
-"waitpid($module, pid, options, /)\n"
+"waitpid($module, /, pid, options=0)\n"
 "--\n"
 "\n"
 "Wait for completion of a given child process.\n"
@@ -2974,19 +2974,21 @@
 "The options argument is ignored on Windows.");
 
 #define OS_WAITPID_METHODDEF    \
-    {"waitpid", (PyCFunction)os_waitpid, METH_VARARGS, os_waitpid__doc__},
+    {"waitpid", (PyCFunction)os_waitpid, METH_FASTCALL, os_waitpid__doc__},
 
 static PyObject *
 os_waitpid_impl(PyObject *module, pid_t pid, int options);
 
 static PyObject *
-os_waitpid(PyObject *module, PyObject *args)
+os_waitpid(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
 {
     PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"pid", "options", NULL};
+    static _PyArg_Parser _parser = {"" _Py_PARSE_PID "|i:waitpid", _keywords, 0};
     pid_t pid;
-    int options;
-
-    if (!PyArg_ParseTuple(args, "" _Py_PARSE_PID "i:waitpid",
+    int options = 0;
+
+    if (!_PyArg_ParseStack(args, nargs, kwnames, &_parser,
         &pid, &options)) {
         goto exit;
     }
@@ -3001,7 +3003,7 @@
 #if defined(HAVE_CWAIT)
 
 PyDoc_STRVAR(os_waitpid__doc__,
-"waitpid($module, pid, options, /)\n"
+"waitpid($module, /, pid, options=0)\n"
 "--\n"
 "\n"
 "Wait for completion of a given process.\n"
@@ -3012,19 +3014,21 @@
 "The options argument is ignored on Windows.");
 
 #define OS_WAITPID_METHODDEF    \
-    {"waitpid", (PyCFunction)os_waitpid, METH_VARARGS, os_waitpid__doc__},
+    {"waitpid", (PyCFunction)os_waitpid, METH_FASTCALL, os_waitpid__doc__},
 
 static PyObject *
 os_waitpid_impl(PyObject *module, intptr_t pid, int options);
 
 static PyObject *
-os_waitpid(PyObject *module, PyObject *args)
+os_waitpid(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
 {
     PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"pid", "options", NULL};
+    static _PyArg_Parser _parser = {"" _Py_PARSE_INTPTR "|i:waitpid", _keywords, 0};
     intptr_t pid;
-    int options;
-
-    if (!PyArg_ParseTuple(args, "" _Py_PARSE_INTPTR "i:waitpid",
+    int options = 0;
+
+    if (!_PyArg_ParseStack(args, nargs, kwnames, &_parser,
         &pid, &options)) {
         goto exit;
     }
@@ -6148,4 +6152,4 @@
 #ifndef OS_GETRANDOM_METHODDEF
     #define OS_GETRANDOM_METHODDEF
 #endif /* !defined(OS_GETRANDOM_METHODDEF) */
-/*[clinic end generated code: output=b9ed5703d2feb0d9 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=271dd33f2c82eb95 input=a9049054013a1b77]*/
diff -r 1c5e0dbcb2a0 Modules/posixmodule.c
--- a/Modules/posixmodule.c	Sun Sep 25 16:54:17 2016 +0300
+++ b/Modules/posixmodule.c	Sun Sep 25 18:41:08 2016 +0200
@@ -6825,8 +6825,7 @@
 /*[clinic input]
 os.waitpid
     pid: pid_t
-    options: int
-    /
+    options: int = 0
 
 Wait for completion of a given child process.
 
@@ -6838,7 +6837,7 @@
 
 static PyObject *
 os_waitpid_impl(PyObject *module, pid_t pid, int options)
-/*[clinic end generated code: output=5c37c06887a20270 input=0bf1666b8758fda3]*/
+/*[clinic end generated code: output=5c37c06887a20270 input=dea600de625eec93]*/
 {
     pid_t res;
     int async_err = 0;
@@ -6860,8 +6859,7 @@
 /*[clinic input]
 os.waitpid
     pid: intptr_t
-    options: int
-    /
+    options: int = 0
 
 Wait for completion of a given process.
 
@@ -6873,7 +6871,7 @@
 
 static PyObject *
 os_waitpid_impl(PyObject *module, intptr_t pid, int options)
-/*[clinic end generated code: output=be836b221271d538 input=40f2440c515410f8]*/
+/*[clinic end generated code: output=be836b221271d538 input=ae2f154feb382cba]*/
 {
     int status;
     intptr_t res;