diff --git a/Doc/c-api/structures.rst b/Doc/c-api/structures.rst
--- a/Doc/c-api/structures.rst
+++ b/Doc/c-api/structures.rst
@@ -148,16 +148,19 @@ specific C type of the *self* object.
 
 The :attr:`ml_flags` field is a bitfield which can include the following flags.
 The individual flags indicate either a calling convention or a binding
 convention.  Of the calling convention flags, only :const:`METH_VARARGS` and
 :const:`METH_KEYWORDS` can be combined (but note that :const:`METH_KEYWORDS`
 alone is equivalent to ``METH_VARARGS | METH_KEYWORDS``). Any of the calling
 convention flags can be combined with a binding flag.
 
+.. versionchanged:: 3.5
+   ``METH_KEYWORDS`` is equivalent to ``METH_VARARGS | METH_KEYWORDS``.
+
 
 .. data:: METH_VARARGS
 
    This is the typical calling convention, where the methods have the type
    :c:type:`PyCFunction`. The function expects two :c:type:`PyObject\*` values.
    The first one is the *self* object for methods; for module functions, it is
    the module object.  The second parameter (often called *args*) is a tuple
    object representing all arguments. This parameter is typically processed
@@ -167,16 +170,18 @@ convention flags can be combined with a 
 .. data:: METH_KEYWORDS
 
    Methods with these flags must be of type :c:type:`PyCFunctionWithKeywords`.
    The function expects three parameters: *self*, *args*, and a dictionary of
    all the keyword arguments.  The flag is typically combined with
    :const:`METH_VARARGS`, and the parameters are typically processed using
    :c:func:`PyArg_ParseTupleAndKeywords`.
 
+   .. versionchanged:: 3.5
+      ``METH_KEYWORDS`` is equivalent to ``METH_VARARGS | METH_KEYWORDS``.
 
 .. data:: METH_NOARGS
 
    Methods without parameters don't need to check whether arguments are given if
    they are listed with the :const:`METH_NOARGS` flag.  They need to be of type
    :c:type:`PyCFunction`.  The first parameter is typically named *self* and will
    hold a reference to the module or object instance.  In all cases the second
    parameter will be *NULL*.
diff --git a/Doc/whatsnew/3.5.rst b/Doc/whatsnew/3.5.rst
--- a/Doc/whatsnew/3.5.rst
+++ b/Doc/whatsnew/3.5.rst
@@ -847,8 +847,11 @@ Changes in the C API
 * Removed non-documented macro :c:macro:`PyObject_REPR` which leaked references.
   Use format character ``%R`` in :c:func:`PyUnicode_FromFormat`-like functions
   to format the :func:`repr` of the object.
 
 * Because the lack of the :attr:`__module__` attribute breaks pickling and
   introspection, a deprecation warning now is raised for builtin type without
   the :attr:`__module__` attribute.  Would be an AttributeError in future.
   (:issue:`20204`)
+
+* :const:`METH_KEYWORDS` is now equivalent to ``METH_VARARGS | METH_KEYWORDS``.
+  (Contributed by Berker Peksag in :issue:`15657`.)
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -3501,16 +3501,30 @@ test_PyTime_AsMicroseconds(PyObject *sel
         return NULL;
     t = _PyTime_FromNanoseconds(ns);
     ms = _PyTime_AsMicroseconds(t, round);
     /* This conversion rely on the fact that _PyTime_t is a number of
        nanoseconds */
     return _PyTime_AsNanosecondsObject(ms);
 }
 
+static PyObject *
+test_meth_keywords(PyObject *self, PyObject *args, PyObject *kwargs)
+{
+    const char *name = NULL;
+
+    static char *kwlist[] = {"name", NULL};
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwargs,
+                    "|s:test_meth_keywords", kwlist, &name))
+        return NULL;
+
+    return Py_BuildValue("s", "OK");
+}
+
 
 static PyMethodDef TestMethods[] = {
     {"raise_exception",         raise_exception,                 METH_VARARGS},
     {"raise_memoryerror",   (PyCFunction)raise_memoryerror,  METH_NOARGS},
     {"test_config",             (PyCFunction)test_config,        METH_NOARGS},
     {"test_sizeof_c_types",     (PyCFunction)test_sizeof_c_types, METH_NOARGS},
     {"test_datetime_capi",  test_datetime_capi,              METH_NOARGS},
     {"test_list_api",           (PyCFunction)test_list_api,      METH_NOARGS},
@@ -3602,16 +3616,17 @@ static PyMethodDef TestMethods[] = {
 #endif
     {"traceback_print",         traceback_print,                 METH_VARARGS},
     {"exception_print",         exception_print,                 METH_VARARGS},
     {"set_exc_info",            test_set_exc_info,               METH_VARARGS},
     {"argparsing",              argparsing,                      METH_VARARGS},
     {"code_newempty",           code_newempty,                   METH_VARARGS},
     {"make_exception_with_doc", (PyCFunction)make_exception_with_doc,
      METH_VARARGS | METH_KEYWORDS},
+    {"test_meth_keywords", (PyCFunction)test_meth_keywords, METH_KEYWORDS},
     {"make_memoryview_from_NULL_pointer", (PyCFunction)make_memoryview_from_NULL_pointer,
      METH_NOARGS},
     {"crash_no_current_thread", (PyCFunction)crash_no_current_thread, METH_NOARGS},
     {"run_in_subinterp",        run_in_subinterp,                METH_VARARGS},
     {"pytime_object_to_time_t", test_pytime_object_to_time_t,  METH_VARARGS},
     {"pytime_object_to_timeval", test_pytime_object_to_timeval,  METH_VARARGS},
     {"pytime_object_to_timespec", test_pytime_object_to_timespec,  METH_VARARGS},
     {"with_tp_del",             with_tp_del,                     METH_VARARGS},
diff --git a/Objects/methodobject.c b/Objects/methodobject.c
--- a/Objects/methodobject.c
+++ b/Objects/methodobject.c
@@ -89,17 +89,17 @@ PyCFunction_Call(PyObject *func, PyObjec
 
     /* PyCFunction_Call() must not be called with an exception set,
        because it may clear it (directly or indirectly) and so the
        caller looses its exception */
     assert(!PyErr_Occurred());
 
     flags = PyCFunction_GET_FLAGS(func) & ~(METH_CLASS | METH_STATIC | METH_COEXIST);
 
-    if (flags == (METH_VARARGS | METH_KEYWORDS)) {
+    if (flags == (METH_VARARGS | METH_KEYWORDS) || flags == METH_KEYWORDS) {
         res = (*(PyCFunctionWithKeywords)meth)(self, args, kwds);
     }
     else {
         if (kwds != NULL && PyDict_Size(kwds) != 0) {
             PyErr_Format(PyExc_TypeError, "%.200s() takes no keyword arguments",
                          f->m_ml->ml_name);
             return NULL;
         }