diff --git a/Include/longobject.h b/Include/longobject.h
index c09565a..5f8b178 100644
--- a/Include/longobject.h
+++ b/Include/longobject.h
@@ -26,6 +26,9 @@
 PyAPI_FUNC(size_t) PyLong_AsSize_t(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLong(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLongMask(PyObject *);
+#ifndef Py_LIMITED_API
+PyAPI_FUNC(int) _PyLong_AsInt(PyObject *);
+#endif
 PyAPI_FUNC(PyObject *) PyLong_GetInfo(void);
 
 /* It may be useful in the future. I've added it in the PyInt -> PyLong
diff --git a/Lib/ctypes/test/test_structures.py b/Lib/ctypes/test/test_structures.py
index b6d8b01..d764ce2 100644
--- a/Lib/ctypes/test/test_structures.py
+++ b/Lib/ctypes/test/test_structures.py
@@ -1,6 +1,7 @@
 import unittest
 from ctypes import *
 from struct import calcsize
+import _testcapi
 
 class SubclassesTest(unittest.TestCase):
     def test_subclass(self):
@@ -199,6 +200,14 @@
              "_pack_": -1}
         self.assertRaises(ValueError, type(Structure), "X", (Structure,), d)
 
+        # Issue 15989
+        d = {"_fields_": [("a", c_byte)],
+             "_pack_": _testcapi.INT_MAX + 1}
+        self.assertRaises(ValueError, type(Structure), "X", (Structure,), d)
+        d = {"_fields_": [("a", c_byte)],
+             "_pack_": _testcapi.UINT_MAX + 2}
+        self.assertRaises(ValueError, type(Structure), "X", (Structure,), d)
+
     def test_initializers(self):
         class Person(Structure):
             _fields_ = [("name", c_char*6),
diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index 413f9dd..6792179 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -5,6 +5,7 @@
 import unittest, string, sys, struct
 from test import support
 from collections import UserList
+import _testcapi
 
 class Sequence:
     def __init__(self, seq='wxyz'): self.seq = seq
@@ -1142,6 +1143,16 @@
         self.checkraises(TypeError, '%10.*f', '__mod__', ('foo', 42.))
         self.checkraises(ValueError, '%10', '__mod__', (42,))
 
+        self.checkraises(OverflowError, '%*s', '__mod__',
+                         (_testcapi.PY_SSIZE_T_MAX + 1, ''))
+        self.checkraises(OverflowError, '%.*f', '__mod__',
+                         (_testcapi.INT_MAX + 1, 1. / 7))
+        # Issue 15989
+        self.checkraises(OverflowError, '%*s', '__mod__',
+                         (1 << (_testcapi.PY_SSIZE_T_MAX.bit_length() + 1), ''))
+        self.checkraises(OverflowError, '%.*f', '__mod__',
+                         (_testcapi.UINT_MAX + 1, 1. / 7))
+
         class X(object): pass
         self.checkraises(TypeError, 'abc', '__mod__', X())
 
diff --git a/Lib/test/test_fcntl.py b/Lib/test/test_fcntl.py
index 29af99c..0ce3a5d 100644
--- a/Lib/test/test_fcntl.py
+++ b/Lib/test/test_fcntl.py
@@ -6,6 +6,7 @@
 import os
 import struct
 import sys
+import _testcapi
 import unittest
 from test.support import verbose, TESTFN, unlink, run_unittest, import_module
 
@@ -76,6 +77,26 @@
             rv = fcntl.fcntl(self.f, fcntl.F_SETLKW, lockdata)
         self.f.close()
 
+    def test_fcntl_bad_file(self):
+        class F:
+            def __init__(self, fn):
+                self.fn = fn
+            def fileno(self):
+                return self.fn
+        self.assertRaises(ValueError, fcntl.fcntl, -1, fcntl.F_SETFL, os.O_NONBLOCK)
+        self.assertRaises(ValueError, fcntl.fcntl, F(-1), fcntl.F_SETFL, os.O_NONBLOCK)
+        self.assertRaises(TypeError, fcntl.fcntl, 'spam', fcntl.F_SETFL, os.O_NONBLOCK)
+        self.assertRaises(TypeError, fcntl.fcntl, F('spam'), fcntl.F_SETFL, os.O_NONBLOCK)
+        # Issue 15989
+        self.assertRaises(OverflowError, fcntl.fcntl, _testcapi.INT_MAX + 1,
+                                                      fcntl.F_SETFL, os.O_NONBLOCK)
+        self.assertRaises(OverflowError, fcntl.fcntl, F(_testcapi.INT_MAX + 1),
+                                                      fcntl.F_SETFL, os.O_NONBLOCK)
+        self.assertRaises(OverflowError, fcntl.fcntl, _testcapi.INT_MIN - 1,
+                                                      fcntl.F_SETFL, os.O_NONBLOCK)
+        self.assertRaises(OverflowError, fcntl.fcntl, F(_testcapi.INT_MIN - 1),
+                                                      fcntl.F_SETFL, os.O_NONBLOCK)
+
     def test_fcntl_64_bit(self):
         # Issue #1309352: fcntl shouldn't fail when the third arg fits in a
         # C 'long' but not in a C 'int'.
diff --git a/Lib/test/test_fileio.py b/Lib/test/test_fileio.py
index b5bd8d4..8267d9e 100644
--- a/Lib/test/test_fileio.py
+++ b/Lib/test/test_fileio.py
@@ -7,6 +7,7 @@
 from array import array
 from weakref import proxy
 from functools import wraps
+import _testcapi
 
 from test.support import TESTFN, check_warnings, run_unittest, make_bad_fd
 from collections import UserList
@@ -346,6 +347,9 @@
         if sys.platform == 'win32':
             import msvcrt
             self.assertRaises(IOError, msvcrt.get_osfhandle, make_bad_fd())
+        # Issue 15989
+        self.assertRaises(TypeError, _FileIO, _testcapi.INT_MAX + 1)
+        self.assertRaises(TypeError, _FileIO, _testcapi.INT_MIN - 1)
 
     def testBadModeArgument(self):
         # verify that we get a sensible error message for bad mode argument
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 56ac2c8..249dc30 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -31,6 +31,7 @@
 import errno
 import warnings
 import pickle
+import _testcapi
 from itertools import cycle, count
 from collections import deque, UserList
 from test import support
@@ -1903,6 +1904,14 @@
         t.write("A\rB")
         self.assertEqual(r.getvalue(), b"XY\nZA\rB")
 
+    # Issue 15989
+    def test_device_encoding(self):
+        b = self.BytesIO()
+        b.fileno = lambda: _testcapi.INT_MAX + 1
+        self.assertRaises(OverflowError, self.TextIOWrapper, b)
+        b.fileno = lambda: _testcapi.UINT_MAX + 1
+        self.assertRaises(OverflowError, self.TextIOWrapper, b)
+
     def test_encoding(self):
         # Check the encoding attribute is always set, and valid
         b = self.BytesIO()
diff --git a/Lib/test/test_poll.py b/Lib/test/test_poll.py
index 7ab3b84..f2d1795 100644
--- a/Lib/test/test_poll.py
+++ b/Lib/test/test_poll.py
@@ -1,6 +1,7 @@
 # Test case for the os.poll() function
 
 import os, select, random, unittest
+import _testcapi
 from test.support import TESTFN, run_unittest
 
 try:
@@ -150,6 +151,15 @@
         if x != 5:
             self.fail('Overflow must have occurred')
 
+        pollster = select.poll()
+        # Issue 15989
+        self.assertRaises(OverflowError, pollster.register, 0,
+                          _testcapi.SHRT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.register, 0,
+                          _testcapi.USHRT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.poll, _testcapi.INT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.poll, _testcapi.UINT_MAX + 1)
+
 def test_main():
     run_unittest(PollTests)
 
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index e40b21e..5573421 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -7,6 +7,7 @@
 import io
 import socket
 import select
+import _testcapi
 import time
 import traceback
 import queue
@@ -850,11 +851,17 @@
             self.assertRaises(ValueError, fp.writable)
             self.assertRaises(ValueError, fp.seekable)
 
-    def testListenBacklog0(self):
+    def test_listen_backlog(self):
+        for backlog in 0, -1:
+            srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+            srv.bind((HOST, 0))
+            srv.listen(backlog)
+            srv.close()
+
+        # Issue 15989
         srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         srv.bind((HOST, 0))
-        # backlog = 0
-        srv.listen(0)
+        self.assertRaises(OverflowError, srv.listen, _testcapi.INT_MAX + 1)
         srv.close()
 
     @unittest.skipUnless(SUPPORTS_IPV6, 'IPv6 required for this test.')
@@ -954,6 +961,11 @@
 
     def _testShutdown(self):
         self.serv_conn.send(MSG)
+        # Issue 15989
+        self.assertRaises(OverflowError, self.serv_conn.shutdown,
+                          _testcapi.INT_MAX + 1)
+        self.assertRaises(OverflowError, self.serv_conn.shutdown,
+                          2 + (_testcapi.UINT_MAX + 1))
         self.serv_conn.shutdown(2)
 
     def testDetach(self):
@@ -1067,7 +1079,10 @@
 
     def testSetBlocking(self):
         # Testing whether set blocking works
-        self.serv.setblocking(0)
+        self.serv.setblocking(True)
+        self.assertIsNone(self.serv.gettimeout())
+        self.serv.setblocking(False)
+        self.assertEqual(self.serv.gettimeout(), 0.0)
         start = time.time()
         try:
             self.serv.accept()
@@ -1075,6 +1090,10 @@
             pass
         end = time.time()
         self.assertTrue((end - start) < 1.0, "Error setting non-blocking mode.")
+        # Issue 15989
+        if _testcapi.UINT_MAX < _testcapi.ULONG_MAX:
+            self.serv.setblocking(_testcapi.UINT_MAX + 1)
+            self.assertIsNone(self.serv.gettimeout())
 
     def _testSetBlocking(self):
         pass
diff --git a/Modules/_ctypes/stgdict.c b/Modules/_ctypes/stgdict.c
index 262d0b4..2338818 100644
--- a/Modules/_ctypes/stgdict.c
+++ b/Modules/_ctypes/stgdict.c
@@ -335,7 +335,7 @@
 
     isPacked = PyObject_GetAttrString(type, "_pack_");
     if (isPacked) {
-        pack = PyLong_AsLong(isPacked);
+        pack = _PyLong_AsInt(isPacked);
         if (pack < 0 || PyErr_Occurred()) {
             Py_XDECREF(isPacked);
             PyErr_SetString(PyExc_ValueError,
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index cec0671..fe91a59 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -303,7 +303,8 @@
     int text = 0, binary = 0, universal = 0;
 
     char rawmode[5], *m;
-    int line_buffering, isatty;
+    int line_buffering;
+    long isatty;
 
     PyObject *raw, *modeobj = NULL, *buffer = NULL, *wrapper = NULL;
 
@@ -441,12 +442,12 @@
 #ifdef HAVE_STRUCT_STAT_ST_BLKSIZE
         {
             struct stat st;
-            long fileno;
+            int fileno;
             PyObject *res = PyObject_CallMethod(raw, "fileno", NULL);
             if (res == NULL)
                 goto error;
 
-            fileno = PyLong_AsLong(res);
+            fileno = _PyLong_AsInt(res);
             Py_DECREF(res);
             if (fileno == -1 && PyErr_Occurred())
                 goto error;
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 8ea7c58..ad4a7e6 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -240,7 +240,7 @@
         return -1;
     }
 
-    fd = PyLong_AsLong(nameobj);
+    fd = _PyLong_AsInt(nameobj);
     if (fd < 0) {
         if (!PyErr_Occurred()) {
             PyErr_SetString(PyExc_ValueError,
diff --git a/Modules/selectmodule.c b/Modules/selectmodule.c
index 0736215..3f846d8 100644
--- a/Modules/selectmodule.c
+++ b/Modules/selectmodule.c
@@ -340,10 +340,13 @@
 
     i = pos = 0;
     while (PyDict_Next(self->dict, &pos, &key, &value)) {
-        self->ufds[i].fd = PyLong_AsLong(key);
+        assert(i < self->ufd_len);
+        /* Never overflow */
+        self->ufds[i].fd = (int)PyLong_AsLong(key);
         self->ufds[i].events = (short)PyLong_AsLong(value);
         i++;
     }
+    assert(i == self->ufd_len);
     self->ufd_uptodate = 1;
     return 1;
 }
@@ -359,10 +362,11 @@
 poll_register(pollObject *self, PyObject *args)
 {
     PyObject *o, *key, *value;
-    int fd, events = POLLIN | POLLPRI | POLLOUT;
+    int fd;
+    short events = POLLIN | POLLPRI | POLLOUT;
     int err;
 
-    if (!PyArg_ParseTuple(args, "O|i:register", &o, &events)) {
+    if (!PyArg_ParseTuple(args, "O|h:register", &o, &events)) {
         return NULL;
     }
 
@@ -501,7 +505,7 @@
         tout = PyNumber_Long(tout);
         if (!tout)
             return NULL;
-        timeout = PyLong_AsLong(tout);
+        timeout = _PyLong_AsInt(tout);
         Py_DECREF(tout);
         if (timeout == -1 && PyErr_Occurred())
             return NULL;
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 4f896fd..bc3372f 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1737,7 +1737,7 @@
 static PyObject *
 sock_setblocking(PySocketSockObject *s, PyObject *arg)
 {
-    int block;
+    long block;
 
     block = PyLong_AsLong(arg);
     if (block == -1 && PyErr_Occurred())
@@ -2219,7 +2219,7 @@
     int backlog;
     int res;
 
-    backlog = PyLong_AsLong(arg);
+    backlog = _PyLong_AsInt(arg);
     if (backlog == -1 && PyErr_Occurred())
         return NULL;
     Py_BEGIN_ALLOW_THREADS
@@ -2822,7 +2822,7 @@
     int how;
     int res;
 
-    how = PyLong_AsLong(arg);
+    how = _PyLong_AsInt(arg);
     if (how == -1 && PyErr_Occurred())
         return NULL;
     Py_BEGIN_ALLOW_THREADS
diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index d20f196..500883e 100644
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -200,7 +200,7 @@
     PyObject *meth;
 
     if (PyLong_Check(o)) {
-        fd = PyLong_AsLong(o);
+        fd = _PyLong_AsInt(o);
     }
     else if ((meth = PyObject_GetAttrString(o, "fileno")) != NULL)
     {
@@ -210,7 +210,7 @@
             return -1;
 
         if (PyLong_Check(fno)) {
-            fd = PyLong_AsLong(fno);
+            fd = _PyLong_AsInt(fno);
             Py_DECREF(fno);
         }
         else {
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 51da329..9ca7b65 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -424,6 +424,24 @@
     return result;
 }
 
+/* Get a C int from a long int object or any object that has an __int__
+   method.  Return -1 and set an error if overflow occurs. */
+
+int
+_PyLong_AsInt(PyObject *obj)
+{
+    int overflow;
+    long result = PyLong_AsLongAndOverflow(obj, &overflow);
+    if (overflow || result > INT_MAX || result < INT_MIN) {
+        /* XXX: could be cute and give a different
+           message for overflow == -1 */
+        PyErr_SetString(PyExc_OverflowError,
+                        "Python int too large to convert to C int");
+        return -1;
+    }
+    return (int)result;
+}
+
 /* Get a Py_ssize_t from a long int object.
    Returns -1 and sets an error condition if overflow occurs. */
 
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index e1df874..80a70b6 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -9640,7 +9640,7 @@
                                     "* wants int");
                     goto onError;
                 }
-                width = PyLong_AsLong(v);
+                width = PyLong_AsSsize_t(v);
                 if (width == -1 && PyErr_Occurred())
                     goto onError;
                 if (width < 0) {
@@ -9677,7 +9677,7 @@
                                         "* wants int");
                         goto onError;
                     }
-                    prec = PyLong_AsLong(v);
+                    prec = _PyLong_AsInt(v);
                     if (prec == -1 && PyErr_Occurred())
                         goto onError;
                     if (prec < 0)