diff --git a/Include/abstract.h b/Include/abstract.h
index cd963af4555..fe089dcbb56 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -1097,6 +1097,9 @@ PyAPI_FUNC(void) _Py_add_one_to_index_F(int nd, Py_ssize_t *index,
                                         const Py_ssize_t *shape);
 PyAPI_FUNC(void) _Py_add_one_to_index_C(int nd, Py_ssize_t *index,
                                         const Py_ssize_t *shape);
+
+/* Convert Python int to Py_ssize_t. Do nothing if the argument is None. */
+PyAPI_FUNC(int) _Py_convert_optional_to_ssize_t(PyObject *, void *);
 #endif /* !Py_LIMITED_API */
 
 
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 0b795c8f22a..bc2fb325976 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -541,30 +541,6 @@ PyNumber_AsOff_t(PyObject *item, PyObject *err)
 }
 
 
-/* Basically the "n" format code with the ability to turn None into -1. */
-int
-_PyIO_ConvertSsize_t(PyObject *obj, void *result) {
-    Py_ssize_t limit;
-    if (obj == Py_None) {
-        limit = -1;
-    }
-    else if (PyIndex_Check(obj)) {
-        limit = PyNumber_AsSsize_t(obj, PyExc_OverflowError);
-        if (limit == -1 && PyErr_Occurred()) {
-            return 0;
-        }
-    }
-    else {
-        PyErr_Format(PyExc_TypeError,
-                     "argument should be integer or None, not '%.200s'",
-                     Py_TYPE(obj)->tp_name);
-        return 0;
-    }
-    *((Py_ssize_t *)result) = limit;
-    return 1;
-}
-
-
 _PyIO_State *
 _PyIO_get_module_state(void)
 {
diff --git a/Modules/_io/_iomodule.h b/Modules/_io/_iomodule.h
index b5f0f5709ef..c589c389b2c 100644
--- a/Modules/_io/_iomodule.h
+++ b/Modules/_io/_iomodule.h
@@ -27,8 +27,6 @@ PyAPI_DATA(PyObject *) _PyWindowsConsoleIO_Type;
 #endif /* MS_WINDOWS */
 #endif /* Py_LIMITED_API */
 
-extern int _PyIO_ConvertSsize_t(PyObject *, void *);
-
 /* These functions are used as METH_NOARGS methods, are normally called
  * with args=NULL, and return a new reference.
  * BUT when args=Py_True is passed, they return a borrowed reference.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index b30d229bb6d..24e052bee2d 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -24,13 +24,6 @@ class _io.BufferedRandom "buffered *" "&PyBufferedRandom_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=59460b9c5639984d]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 _Py_IDENTIFIER(close);
 _Py_IDENTIFIER(_dealloc_warn);
 _Py_IDENTIFIER(flush);
@@ -892,13 +885,13 @@ end:
 
 /*[clinic input]
 _io._Buffered.read
-    size as n: io_ssize_t = -1
+    size as n: Py_ssize_t(accept={int, NoneType}) = -1
     /
 [clinic start generated code]*/
 
 static PyObject *
 _io__Buffered_read_impl(buffered *self, Py_ssize_t n)
-/*[clinic end generated code: output=f41c78bb15b9bbe9 input=c0939ec7f9e9354f]*/
+/*[clinic end generated code: output=f41c78bb15b9bbe9 input=7df81e82e08a68a2]*/
 {
     PyObject *res;
 
@@ -1206,13 +1199,13 @@ end_unlocked:
 
 /*[clinic input]
 _io._Buffered.readline
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 [clinic start generated code]*/
 
 static PyObject *
 _io__Buffered_readline_impl(buffered *self, Py_ssize_t size)
-/*[clinic end generated code: output=24dd2aa6e33be83c input=ff1e0df821cb4e5c]*/
+/*[clinic end generated code: output=24dd2aa6e33be83c input=673b6240e315ef8a]*/
 {
     CHECK_INITIALIZED(self)
     return _buffered_readline(self, size);
diff --git a/Modules/_io/bytesio.c b/Modules/_io/bytesio.c
index f78b4475d00..42c7f7933e0 100644
--- a/Modules/_io/bytesio.c
+++ b/Modules/_io/bytesio.c
@@ -8,13 +8,6 @@ class _io.BytesIO "bytesio *" "&PyBytesIO_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=7f50ec034f5c0b26]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 typedef struct {
     PyObject_HEAD
     PyObject *buf;
@@ -381,7 +374,7 @@ read_bytes(bytesio *self, Py_ssize_t size)
 
 /*[clinic input]
 _io.BytesIO.read
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read at most size bytes, returned as a bytes object.
@@ -392,7 +385,7 @@ Return an empty bytes object at EOF.
 
 static PyObject *
 _io_BytesIO_read_impl(bytesio *self, Py_ssize_t size)
-/*[clinic end generated code: output=9cc025f21c75bdd2 input=c81ec53b8f2cc3cf]*/
+/*[clinic end generated code: output=9cc025f21c75bdd2 input=74344a39f431c3d7]*/
 {
     Py_ssize_t n;
 
@@ -412,7 +405,7 @@ _io_BytesIO_read_impl(bytesio *self, Py_ssize_t size)
 
 /*[clinic input]
 _io.BytesIO.read1
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read at most size bytes, returned as a bytes object.
@@ -423,14 +416,14 @@ Return an empty bytes object at EOF.
 
 static PyObject *
 _io_BytesIO_read1_impl(bytesio *self, Py_ssize_t size)
-/*[clinic end generated code: output=d0f843285aa95f1c input=67cf18b142111664]*/
+/*[clinic end generated code: output=d0f843285aa95f1c input=440a395bf9129ef5]*/
 {
     return _io_BytesIO_read_impl(self, size);
 }
 
 /*[clinic input]
 _io.BytesIO.readline
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Next line from the file, as a bytes object.
@@ -442,7 +435,7 @@ Return an empty bytes object at EOF.
 
 static PyObject *
 _io_BytesIO_readline_impl(bytesio *self, Py_ssize_t size)
-/*[clinic end generated code: output=4bff3c251df8ffcd input=7c95bd3f9e9d1646]*/
+/*[clinic end generated code: output=4bff3c251df8ffcd input=e7c3fbd1744e2783]*/
 {
     Py_ssize_t n;
 
@@ -556,7 +549,7 @@ _io_BytesIO_readinto_impl(bytesio *self, Py_buffer *buffer)
 
 /*[clinic input]
 _io.BytesIO.truncate
-    size as arg: object = None
+    size: Py_ssize_t(accept={int, NoneType}, c_default="self->pos") = None
     /
 
 Truncate the file to at most size bytes.
@@ -566,31 +559,12 @@ The current file position is unchanged.  Returns the new size.
 [clinic start generated code]*/
 
 static PyObject *
-_io_BytesIO_truncate_impl(bytesio *self, PyObject *arg)
-/*[clinic end generated code: output=81e6be60e67ddd66 input=11ed1966835462ba]*/
+_io_BytesIO_truncate_impl(bytesio *self, Py_ssize_t size)
+/*[clinic end generated code: output=9ad17650c15fa09b input=423759dd42d2f7c1]*/
 {
-    Py_ssize_t size;
-
     CHECK_CLOSED(self);
     CHECK_EXPORTS(self);
 
-    if (arg == Py_None) {
-        /* Truncate to current position if no argument is passed. */
-        size = self->pos;
-    }
-    else if (PyIndex_Check(arg)) {
-        size = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
-        if (size == -1 && PyErr_Occurred()) {
-            return NULL;
-        }
-    }
-    else {
-        PyErr_Format(PyExc_TypeError,
-                     "argument should be integer or None, not '%.200s'",
-                     Py_TYPE(arg)->tp_name);
-        return NULL;
-    }
-
     if (size < 0) {
         PyErr_Format(PyExc_ValueError,
                      "negative size value %zd", size);
diff --git a/Modules/_io/clinic/bufferedio.c.h b/Modules/_io/clinic/bufferedio.c.h
index 4337ecfaa99..c910dcee372 100644
--- a/Modules/_io/clinic/bufferedio.c.h
+++ b/Modules/_io/clinic/bufferedio.c.h
@@ -134,7 +134,7 @@ _io__Buffered_read(buffered *self, PyObject **args, Py_ssize_t nargs, PyObject *
     Py_ssize_t n = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read",
-        _PyIO_ConvertSsize_t, &n)) {
+        _Py_convert_optional_to_ssize_t, &n)) {
         goto exit;
     }
 
@@ -258,7 +258,7 @@ _io__Buffered_readline(buffered *self, PyObject **args, Py_ssize_t nargs, PyObje
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:readline",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -500,4 +500,4 @@ _io_BufferedRandom___init__(PyObject *self, PyObject *args, PyObject *kwargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=e37b969b1acaa09c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=3cf3262c9b157dc1 input=a9049054013a1b77]*/
diff --git a/Modules/_io/clinic/bytesio.c.h b/Modules/_io/clinic/bytesio.c.h
index 60b7eaadd02..559971c4a4b 100644
--- a/Modules/_io/clinic/bytesio.c.h
+++ b/Modules/_io/clinic/bytesio.c.h
@@ -170,7 +170,7 @@ _io_BytesIO_read(bytesio *self, PyObject **args, Py_ssize_t nargs, PyObject *kwn
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -205,7 +205,7 @@ _io_BytesIO_read1(bytesio *self, PyObject **args, Py_ssize_t nargs, PyObject *kw
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read1",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -241,7 +241,7 @@ _io_BytesIO_readline(bytesio *self, PyObject **args, Py_ssize_t nargs, PyObject
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:readline",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -339,24 +339,23 @@ PyDoc_STRVAR(_io_BytesIO_truncate__doc__,
     {"truncate", (PyCFunction)_io_BytesIO_truncate, METH_FASTCALL, _io_BytesIO_truncate__doc__},
 
 static PyObject *
-_io_BytesIO_truncate_impl(bytesio *self, PyObject *arg);
+_io_BytesIO_truncate_impl(bytesio *self, Py_ssize_t size);
 
 static PyObject *
 _io_BytesIO_truncate(bytesio *self, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
 {
     PyObject *return_value = NULL;
-    PyObject *arg = Py_None;
+    Py_ssize_t size = self->pos;
 
-    if (!_PyArg_UnpackStack(args, nargs, "truncate",
-        0, 1,
-        &arg)) {
+    if (!_PyArg_ParseStack(args, nargs, "|O&:truncate",
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
     if (!_PyArg_NoStackKeywords("truncate", kwnames)) {
         goto exit;
     }
-    return_value = _io_BytesIO_truncate_impl(self, arg);
+    return_value = _io_BytesIO_truncate_impl(self, size);
 
 exit:
     return return_value;
@@ -469,4 +468,4 @@ _io_BytesIO___init__(PyObject *self, PyObject *args, PyObject *kwargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=74a856733a5d55b0 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=733795434f838b71 input=a9049054013a1b77]*/
diff --git a/Modules/_io/clinic/fileio.c.h b/Modules/_io/clinic/fileio.c.h
index 7a8e2c64c35..cd5075db124 100644
--- a/Modules/_io/clinic/fileio.c.h
+++ b/Modules/_io/clinic/fileio.c.h
@@ -214,7 +214,7 @@ _io_FileIO_read(fileio *self, PyObject **args, Py_ssize_t nargs, PyObject *kwnam
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -385,4 +385,4 @@ _io_FileIO_isatty(fileio *self, PyObject *Py_UNUSED(ignored))
 #ifndef _IO_FILEIO_TRUNCATE_METHODDEF
     #define _IO_FILEIO_TRUNCATE_METHODDEF
 #endif /* !defined(_IO_FILEIO_TRUNCATE_METHODDEF) */
-/*[clinic end generated code: output=034d782a0daa82bd input=a9049054013a1b77]*/
+/*[clinic end generated code: output=a4044e2d878248d0 input=a9049054013a1b77]*/
diff --git a/Modules/_io/clinic/iobase.c.h b/Modules/_io/clinic/iobase.c.h
index 045bb3b6991..a6780c27a7f 100644
--- a/Modules/_io/clinic/iobase.c.h
+++ b/Modules/_io/clinic/iobase.c.h
@@ -186,7 +186,7 @@ _io__IOBase_readline(PyObject *self, PyObject **args, Py_ssize_t nargs, PyObject
     Py_ssize_t limit = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:readline",
-        _PyIO_ConvertSsize_t, &limit)) {
+        _Py_convert_optional_to_ssize_t, &limit)) {
         goto exit;
     }
 
@@ -222,7 +222,7 @@ _io__IOBase_readlines(PyObject *self, PyObject **args, Py_ssize_t nargs, PyObjec
     Py_ssize_t hint = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:readlines",
-        _PyIO_ConvertSsize_t, &hint)) {
+        _Py_convert_optional_to_ssize_t, &hint)) {
         goto exit;
     }
 
@@ -291,4 +291,4 @@ _io__RawIOBase_readall(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
     return _io__RawIOBase_readall_impl(self);
 }
-/*[clinic end generated code: output=1bcece367fc7b0cd input=a9049054013a1b77]*/
+/*[clinic end generated code: output=d3f59c135231baae input=a9049054013a1b77]*/
diff --git a/Modules/_io/clinic/stringio.c.h b/Modules/_io/clinic/stringio.c.h
index 362d0b9d4cc..2710135e277 100644
--- a/Modules/_io/clinic/stringio.c.h
+++ b/Modules/_io/clinic/stringio.c.h
@@ -60,7 +60,7 @@ _io_StringIO_read(stringio *self, PyObject **args, Py_ssize_t nargs, PyObject *k
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -94,7 +94,7 @@ _io_StringIO_readline(stringio *self, PyObject **args, Py_ssize_t nargs, PyObjec
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:readline",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -121,24 +121,23 @@ PyDoc_STRVAR(_io_StringIO_truncate__doc__,
     {"truncate", (PyCFunction)_io_StringIO_truncate, METH_FASTCALL, _io_StringIO_truncate__doc__},
 
 static PyObject *
-_io_StringIO_truncate_impl(stringio *self, PyObject *arg);
+_io_StringIO_truncate_impl(stringio *self, Py_ssize_t size);
 
 static PyObject *
 _io_StringIO_truncate(stringio *self, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
 {
     PyObject *return_value = NULL;
-    PyObject *arg = Py_None;
+    Py_ssize_t size = self->pos;
 
-    if (!_PyArg_UnpackStack(args, nargs, "truncate",
-        0, 1,
-        &arg)) {
+    if (!_PyArg_ParseStack(args, nargs, "|O&:truncate",
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
     if (!_PyArg_NoStackKeywords("truncate", kwnames)) {
         goto exit;
     }
-    return_value = _io_StringIO_truncate_impl(self, arg);
+    return_value = _io_StringIO_truncate_impl(self, size);
 
 exit:
     return return_value;
@@ -303,4 +302,4 @@ _io_StringIO_seekable(stringio *self, PyObject *Py_UNUSED(ignored))
 {
     return _io_StringIO_seekable_impl(self);
 }
-/*[clinic end generated code: output=965fe9cb0d11511a input=a9049054013a1b77]*/
+/*[clinic end generated code: output=03429d95ed7cd92f input=a9049054013a1b77]*/
diff --git a/Modules/_io/clinic/textio.c.h b/Modules/_io/clinic/textio.c.h
index 46b3edafa92..4eab136f772 100644
--- a/Modules/_io/clinic/textio.c.h
+++ b/Modules/_io/clinic/textio.c.h
@@ -237,7 +237,7 @@ _io_TextIOWrapper_read(textio *self, PyObject **args, Py_ssize_t nargs, PyObject
     Py_ssize_t n = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read",
-        _PyIO_ConvertSsize_t, &n)) {
+        _Py_convert_optional_to_ssize_t, &n)) {
         goto exit;
     }
 
@@ -480,4 +480,4 @@ _io_TextIOWrapper_close(textio *self, PyObject *Py_UNUSED(ignored))
 {
     return _io_TextIOWrapper_close_impl(self);
 }
-/*[clinic end generated code: output=67eba50449900a96 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=8e5c21c88c7c70bc input=a9049054013a1b77]*/
diff --git a/Modules/_io/clinic/winconsoleio.c.h b/Modules/_io/clinic/winconsoleio.c.h
index f568053d63a..f694cd8cc88 100644
--- a/Modules/_io/clinic/winconsoleio.c.h
+++ b/Modules/_io/clinic/winconsoleio.c.h
@@ -221,7 +221,7 @@ _io__WindowsConsoleIO_read(winconsoleio *self, PyObject **args, Py_ssize_t nargs
     Py_ssize_t size = -1;
 
     if (!_PyArg_ParseStack(args, nargs, "|O&:read",
-        _PyIO_ConvertSsize_t, &size)) {
+        _Py_convert_optional_to_ssize_t, &size)) {
         goto exit;
     }
 
@@ -332,4 +332,4 @@ _io__WindowsConsoleIO_isatty(winconsoleio *self, PyObject *Py_UNUSED(ignored))
 #ifndef _IO__WINDOWSCONSOLEIO_ISATTY_METHODDEF
     #define _IO__WINDOWSCONSOLEIO_ISATTY_METHODDEF
 #endif /* !defined(_IO__WINDOWSCONSOLEIO_ISATTY_METHODDEF) */
-/*[clinic end generated code: output=04dab03363f5e304 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=f2a240ec6af12a20 input=a9049054013a1b77]*/
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 60005083ff2..3c0b7529323 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -52,13 +52,6 @@ class _io.FileIO "fileio *" "&PyFileIO_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=1c77708b41fda70c]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 typedef struct {
     PyObject_HEAD
     int fd;
@@ -770,7 +763,7 @@ _io_FileIO_readall_impl(fileio *self)
 
 /*[clinic input]
 _io.FileIO.read
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read at most size bytes, returned as bytes.
@@ -782,7 +775,7 @@ Return an empty bytes object at EOF.
 
 static PyObject *
 _io_FileIO_read_impl(fileio *self, Py_ssize_t size)
-/*[clinic end generated code: output=42528d39dd0ca641 input=5c6caa5490c13a9b]*/
+/*[clinic end generated code: output=42528d39dd0ca641 input=bec9a2c704ddcbc9]*/
 {
     char *ptr;
     Py_ssize_t n;
diff --git a/Modules/_io/iobase.c b/Modules/_io/iobase.c
index b176457e0d9..75cfe59624b 100644
--- a/Modules/_io/iobase.c
+++ b/Modules/_io/iobase.c
@@ -20,13 +20,6 @@ class _io._RawIOBase "PyObject *" "&PyRawIOBase_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=d29a4d076c2b211c]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 /*
  * IOBase class, an abstract class
  */
@@ -488,7 +481,7 @@ _io__IOBase_isatty_impl(PyObject *self)
 
 /*[clinic input]
 _io._IOBase.readline
-    size as limit: io_ssize_t = -1
+    size as limit: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read and return a line from the stream.
@@ -502,7 +495,7 @@ terminator(s) recognized.
 
 static PyObject *
 _io__IOBase_readline_impl(PyObject *self, Py_ssize_t limit)
-/*[clinic end generated code: output=4479f79b58187840 input=df4cc8884f553cab]*/
+/*[clinic end generated code: output=4479f79b58187840 input=d0c596794e877bff]*/
 {
     /* For backwards compatibility, a (slowish) readline(). */
 
@@ -635,7 +628,7 @@ iobase_iternext(PyObject *self)
 
 /*[clinic input]
 _io._IOBase.readlines
-    hint: io_ssize_t = -1
+    hint: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Return a list of lines from the stream.
@@ -647,7 +640,7 @@ lines so far exceeds hint.
 
 static PyObject *
 _io__IOBase_readlines_impl(PyObject *self, Py_ssize_t hint)
-/*[clinic end generated code: output=2f50421677fa3dea input=1961c4a95e96e661]*/
+/*[clinic end generated code: output=2f50421677fa3dea input=9400c786ea9dc416]*/
 {
     Py_ssize_t length = 0;
     PyObject *result;
diff --git a/Modules/_io/stringio.c b/Modules/_io/stringio.c
index ef450328fa3..2ec32acfcb8 100644
--- a/Modules/_io/stringio.c
+++ b/Modules/_io/stringio.c
@@ -17,13 +17,6 @@ class _io.StringIO "stringio *" "&PyStringIO_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=c17bc0f42165cd7d]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 typedef struct {
     PyObject_HEAD
     Py_UCS4 *buf;
@@ -308,7 +301,7 @@ _io_StringIO_tell_impl(stringio *self)
 
 /*[clinic input]
 _io.StringIO.read
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read at most size characters, returned as a string.
@@ -319,7 +312,7 @@ is reached. Return an empty string at EOF.
 
 static PyObject *
 _io_StringIO_read_impl(stringio *self, Py_ssize_t size)
-/*[clinic end generated code: output=ae8cf6002f71626c input=bbd84248eb4ab957]*/
+/*[clinic end generated code: output=ae8cf6002f71626c input=0921093383dfb92d]*/
 {
     Py_ssize_t n;
     Py_UCS4 *output;
@@ -380,7 +373,7 @@ _stringio_readline(stringio *self, Py_ssize_t limit)
 
 /*[clinic input]
 _io.StringIO.readline
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read until newline or EOF.
@@ -390,7 +383,7 @@ Returns an empty string if EOF is hit immediately.
 
 static PyObject *
 _io_StringIO_readline_impl(stringio *self, Py_ssize_t size)
-/*[clinic end generated code: output=cabd6452f1b7e85d input=04de7535f732cb3d]*/
+/*[clinic end generated code: output=cabd6452f1b7e85d input=a5bd70bf682aa276]*/
 {
     CHECK_INITIALIZED(self);
     CHECK_CLOSED(self);
@@ -439,7 +432,7 @@ stringio_iternext(stringio *self)
 
 /*[clinic input]
 _io.StringIO.truncate
-    pos as arg: object = None
+    pos as size: Py_ssize_t(accept={int, NoneType}, c_default="self->pos") = None
     /
 
 Truncate size to pos.
@@ -450,31 +443,12 @@ Returns the new absolute position.
 [clinic start generated code]*/
 
 static PyObject *
-_io_StringIO_truncate_impl(stringio *self, PyObject *arg)
-/*[clinic end generated code: output=6072439c2b01d306 input=748619a494ba53ad]*/
+_io_StringIO_truncate_impl(stringio *self, Py_ssize_t size)
+/*[clinic end generated code: output=eb3aef8e06701365 input=5505cff90ca48b96]*/
 {
-    Py_ssize_t size;
-
     CHECK_INITIALIZED(self);
     CHECK_CLOSED(self);
 
-    if (PyIndex_Check(arg)) {
-        size = PyNumber_AsSsize_t(arg, PyExc_OverflowError);
-        if (size == -1 && PyErr_Occurred()) {
-            return NULL;
-        }
-    }
-    else if (arg == Py_None) {
-        /* Truncate to current position if no argument is passed. */
-        size = self->pos;
-    }
-    else {
-        PyErr_Format(PyExc_TypeError,
-                     "argument should be integer or None, not '%.200s'",
-                     Py_TYPE(arg)->tp_name);
-        return NULL;
-    }
-
     if (size < 0) {
         PyErr_Format(PyExc_ValueError,
                      "Negative size value %zd", size);
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index 0211ad95860..5639ad8bfb4 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -18,13 +18,6 @@ class _io.TextIOWrapper "textio *" "&TextIOWrapper_TYpe"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=2097a4fc85670c26]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 _Py_IDENTIFIER(close);
 _Py_IDENTIFIER(_dealloc_warn);
 _Py_IDENTIFIER(decode);
@@ -1529,13 +1522,13 @@ textiowrapper_read_chunk(textio *self, Py_ssize_t size_hint)
 
 /*[clinic input]
 _io.TextIOWrapper.read
-    size as n: io_ssize_t = -1
+    size as n: Py_ssize_t(accept={int, NoneType}) = -1
     /
 [clinic start generated code]*/
 
 static PyObject *
 _io_TextIOWrapper_read_impl(textio *self, Py_ssize_t n)
-/*[clinic end generated code: output=7e651ce6cc6a25a6 input=8c09398424085cca]*/
+/*[clinic end generated code: output=7e651ce6cc6a25a6 input=123eecbfe214aeb8]*/
 {
     PyObject *result = NULL, *chunks = NULL;
 
diff --git a/Modules/_io/winconsoleio.c b/Modules/_io/winconsoleio.c
index 4251c202414..814462f7c98 100644
--- a/Modules/_io/winconsoleio.c
+++ b/Modules/_io/winconsoleio.c
@@ -140,13 +140,6 @@ class _io._WindowsConsoleIO "winconsoleio *" "&PyWindowsConsoleIO_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=e897fdc1fba4e131]*/
 
-/*[python input]
-class io_ssize_t_converter(CConverter):
-    type = 'Py_ssize_t'
-    converter = '_PyIO_ConvertSsize_t'
-[python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=d0a811d3cbfd1b33]*/
-
 typedef struct {
     PyObject_HEAD
     HANDLE handle;
@@ -906,7 +899,7 @@ _io__WindowsConsoleIO_readall_impl(winconsoleio *self)
 
 /*[clinic input]
 _io._WindowsConsoleIO.read
-    size: io_ssize_t = -1
+    size: Py_ssize_t(accept={int, NoneType}) = -1
     /
 
 Read at most size bytes, returned as bytes.
@@ -918,7 +911,7 @@ Return an empty bytes object at EOF.
 
 static PyObject *
 _io__WindowsConsoleIO_read_impl(winconsoleio *self, Py_ssize_t size)
-/*[clinic end generated code: output=57df68af9f4b22d0 input=6c56fceec460f1dd]*/
+/*[clinic end generated code: output=57df68af9f4b22d0 input=8bc73bc15d0fa072]*/
 {
     PyObject *bytes;
     Py_ssize_t bytes_size;
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 7c15d377cfd..56f44006704 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -240,29 +240,6 @@ mmap_read_line_method(mmap_object *self,
     return result;
 }
 
-/* Basically the "n" format code with the ability to turn None into -1. */
-static int
-mmap_convert_ssize_t(PyObject *obj, void *result) {
-    Py_ssize_t limit;
-    if (obj == Py_None) {
-        limit = -1;
-    }
-    else if (PyIndex_Check(obj)) {
-        limit = PyNumber_AsSsize_t(obj, PyExc_OverflowError);
-        if (limit == -1 && PyErr_Occurred()) {
-            return 0;
-        }
-    }
-    else {
-        PyErr_Format(PyExc_TypeError,
-                     "argument should be integer or None, not '%.200s'",
-                     Py_TYPE(obj)->tp_name);
-        return 0;
-    }
-    *((Py_ssize_t *)result) = limit;
-    return 1;
-}
-
 static PyObject *
 mmap_read_method(mmap_object *self,
                  PyObject *args)
@@ -271,7 +248,7 @@ mmap_read_method(mmap_object *self,
     PyObject *result;
 
     CHECK_VALID(NULL);
-    if (!PyArg_ParseTuple(args, "|O&:read", mmap_convert_ssize_t, &num_bytes))
+    if (!PyArg_ParseTuple(args, "|O&:read", _Py_convert_optional_to_ssize_t, &num_bytes))
         return(NULL);
 
     /* silently 'adjust' out-of-range requests */
diff --git a/Python/modsupport.c b/Python/modsupport.c
index 9637191feb8..8a77a7b06dc 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -12,6 +12,31 @@ static PyObject **va_build_stack(PyObject **small_stack, Py_ssize_t small_stack_
 /* Package context -- the full module name for package imports */
 const char *_Py_PackageContext = NULL;
 
+
+int
+_Py_convert_optional_to_ssize_t(PyObject *obj, void *result)
+{
+    Py_ssize_t limit;
+    if (obj == Py_None) {
+        return 1;
+    }
+    else if (PyIndex_Check(obj)) {
+        limit = PyNumber_AsSsize_t(obj, PyExc_OverflowError);
+        if (limit == -1 && PyErr_Occurred()) {
+            return 0;
+        }
+    }
+    else {
+        PyErr_Format(PyExc_TypeError,
+                     "argument should be integer or None, not '%.200s'",
+                     Py_TYPE(obj)->tp_name);
+        return 0;
+    }
+    *((Py_ssize_t *)result) = limit;
+    return 1;
+}
+
+
 /* Helper for mkvalue() to scan the length of a format */
 
 static Py_ssize_t
diff --git a/Tools/clinic/clinic.py b/Tools/clinic/clinic.py
index 53108b17eee..1d570f17c35 100755
--- a/Tools/clinic/clinic.py
+++ b/Tools/clinic/clinic.py
@@ -2650,12 +2650,20 @@ class unsigned_long_long_converter(CConverter):
         if not bitwise:
             fail("Unsigned long long must be bitwise (for now).")
 
+
 class Py_ssize_t_converter(CConverter):
     type = 'Py_ssize_t'
-    default_type = int
-    format_unit = 'n'
     c_ignored_default = "0"
 
+    def converter_init(self, *, accept={int}):
+        if accept == {int}:
+            self.format_unit = 'n'
+            self.default_type = int
+        elif accept == {int, NoneType}:
+            self.converter = '_Py_convert_optional_to_ssize_t'
+        else:
+            fail("Py_ssize_t_converter: illegal 'accept' argument " + repr(accept))
+
 
 class slice_index_converter(CConverter):
     type = 'Py_ssize_t'