diff -r 6f1602dfa4d5 Include/fileutils.h
--- a/Include/fileutils.h	Fri Oct 21 19:53:30 2016 +0900
+++ b/Include/fileutils.h	Fri Oct 21 16:24:30 2016 +0200
@@ -17,6 +17,14 @@
 
 PyAPI_FUNC(PyObject *) _Py_device_encoding(int);
 
+#if defined(MS_WINDOWS) || defined(__APPLE__)
+#define _PY_READ_MAX  INT_MAX
+#define _PY_WRITE_MAX INT_MAX 
+#else
+#define _PY_READ_MAX  PY_SSIZE_T_MAX
+#define _PY_WRITE_MAX PY_SSIZE_T_MAX
+#endif
+
 #ifdef MS_WINDOWS
 struct _Py_stat_struct {
     unsigned long st_dev;
diff -r 6f1602dfa4d5 Lib/test/test_largefile.py
--- a/Lib/test/test_largefile.py	Fri Oct 21 19:53:30 2016 +0900
+++ b/Lib/test/test_largefile.py	Fri Oct 21 16:24:30 2016 +0200
@@ -5,6 +5,7 @@
 import stat
 import sys
 import unittest
+from test import support
 from test.support import TESTFN, requires, unlink
 import io  # C implementation of io
 import _pyio as pyio # Python implementation of io
@@ -16,6 +17,7 @@
     """Test that each file function works as expected for large
     (i.e. > 2GB) files.
     """
+    LARGE = 2**31
 
     def setUp(self):
         if os.path.exists(TESTFN):
@@ -44,6 +46,22 @@
         if not os.stat(TESTFN)[stat.ST_SIZE] == 0:
             raise cls.failureException('File was not truncated by opening '
                                        'with mode "wb"')
+    def test_large_writes(self):
+        support.requires('largefile',
+            'test requires %s bytes and a long time to run' % self.LARGE)
+        with self.open(support.TESTFN, "wb") as f:
+            b = bytearray(self.LARGE)
+            self.assertEqual(f.write(b), self.LARGE)
+
+    def test_large_reads(self):
+        support.requires('largefile',
+            'test requires %s bytes and a long time to run' % self.LARGE)
+        with self.open(support.TESTFN, "wb") as f:
+            b = bytearray(self.LARGE)
+            self.assertEqual(f.write(b), self.LARGE)
+
+        with self.open(support.TESTFN, "rb") as f:
+            self.assertEqual(f.read(self.LARGE), self.LARGE)
 
     def test_osstat(self):
         self.assertEqual(os.stat(TESTFN)[stat.ST_SIZE], size+1)
diff -r 6f1602dfa4d5 Modules/_io/fileio.c
--- a/Modules/_io/fileio.c	Fri Oct 21 19:53:30 2016 +0900
+++ b/Modules/_io/fileio.c	Fri Oct 21 16:24:30 2016 +0200
@@ -796,11 +796,8 @@
     if (size < 0)
         return _io_FileIO_readall_impl(self);
 
-#ifdef MS_WINDOWS
-    /* On Windows, the count parameter of read() is an int */
-    if (size > INT_MAX)
-        size = INT_MAX;
-#endif
+    if (size > _PY_READ_MAX)
+        size = _PY_READ_MAX;
 
     bytes = PyBytes_FromStringAndSize(NULL, size);
     if (bytes == NULL)
diff -r 6f1602dfa4d5 Python/fileutils.c
--- a/Python/fileutils.c	Fri Oct 21 19:53:30 2016 +0900
+++ b/Python/fileutils.c	Fri Oct 21 16:24:30 2016 +0200
@@ -1175,18 +1175,9 @@
      * handler raised an exception. */
     assert(!PyErr_Occurred());
 
-#ifdef MS_WINDOWS
-    if (count > INT_MAX) {
-        /* On Windows, the count parameter of read() is an int */
-        count = INT_MAX;
+    if (count > _PY_READ_MAX) {
+        count = _PY_READ_MAX;
     }
-#else
-    if (count > PY_SSIZE_T_MAX) {
-        /* if count is greater than PY_SSIZE_T_MAX,
-         * read() result is undefined */
-        count = PY_SSIZE_T_MAX;
-    }
-#endif
 
     _Py_BEGIN_SUPPRESS_IPH
     do {
@@ -1237,15 +1228,10 @@
            depending on heap usage). */
         count = 32767;
     }
-    else if (count > INT_MAX)
-        count = INT_MAX;
-#else
-    if (count > PY_SSIZE_T_MAX) {
-        /* write() should truncate count to PY_SSIZE_T_MAX, but it's safer
-         * to do it ourself to have a portable behaviour. */
-        count = PY_SSIZE_T_MAX;
+#endif
+    if (count > _PY_WRITE_MAX) {
+        count = _PY_WRITE_MAX;
     }
-#endif
 
     if (gil_held) {
         do {