diff -r 4d4277941a45 Lib/test/test_fileio.py
--- a/Lib/test/test_fileio.py	Fri Apr 12 23:30:59 2013 +0300
+++ b/Lib/test/test_fileio.py	Sat Apr 13 17:09:35 2013 -0400
@@ -449,6 +449,21 @@
         self.assertRaises(MyException, MyFileIO, fd)
         os.close(fd)  # should not raise OSError(EBADF)
 
+    def testWin32_crt_write(self):
+        """ text / binary mode shouldn't change if fdopen is used. """
+
+        if sys.platform != 'win32':
+            return
+
+        fd = os.open(TESTFN, os.O_WRONLY | os.O_CREAT | os.O_TEXT)
+        f = os.fdopen(fd, 'w')
+        os.write(fd, b'\n')
+        f.close()
+
+        with open(TESTFN, 'rb') as f:
+            self.assertEqual(f.read(), b'\r\n')
+
+        assert False
 
 def test_main():
     # Historically, these tests have been sloppy about removing TESTFN.
diff -r 4d4277941a45 Modules/_io/fileio.c
--- a/Modules/_io/fileio.c	Fri Apr 12 23:30:59 2013 +0300
+++ b/Modules/_io/fileio.c	Sat Apr 13 17:09:35 2013 -0400
@@ -33,6 +33,13 @@
 #define HAVE_FTRUNCATE
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
+
+#define USE_WIN32_READWRITEFILE
+#ifdef USE_WIN32_READWRITEFILE
+/* Undocumented CRT api for setting errno from GetLastError()
+   used to match the behavior of the CRT's read and write */
+extern void _dosmaperr(unsigned long error_code);
+#endif
 #endif
 
 #if BUFSIZ < (8*1024)
@@ -202,6 +209,78 @@
     return 0;
 }
 
+static Py_ssize_t
+internal_read(int fd, void* buffer, Py_ssize_t len)
+{
+    Py_ssize_t n;
+
+#if defined(USE_WIN32_READWRITEFILE)
+    HANDLE handle = (HANDLE) _get_osfhandle(fd);
+    DWORD bytes_read;
+
+    if (len > INT_MAX)
+        len = INT_MAX;
+
+    if (handle == INVALID_HANDLE_VALUE)
+        /* _get_osfhandle sets errno in invalid case */
+        return 0;
+    if (!ReadFile(handle, buffer, len, &bytes_read, NULL))
+        _dosmaperr(GetLastError());
+    n = bytes_read;
+#elif defined(MS_WIN64) || defined(MS_WINDOWS)
+    if (len > INT_MAX)
+        len = INT_MAX;
+    n = read(fd, buffer, (int)len);
+#else
+    n = read(fd, buffer, len);
+#endif
+
+    return n;
+}
+
+static Py_ssize_t
+internal_write(int fd, void* buffer, Py_ssize_t len)
+{
+    Py_ssize_t n;
+#if defined(USE_WIN32_READWRITEFILE)
+    HANDLE handle = (HANDLE) _get_osfhandle(fd);
+    DWORD bytes_written;
+
+    if (handle == INVALID_HANDLE_VALUE)
+        /* _get_osfhandle sets errno in invalid case */
+        return 0;
+
+    if (len > 32767 && isatty(fd)) {
+        /* Issue #11395: the Windows console returns an error (12: not
+           enough space error) on writing into stdout if stdout mode is
+           binary and the length is greater than 66,000 bytes (or less,
+        depending on heap usage). */
+        len = 32767;
+    }
+    else if (len > INT_MAX)
+        len = INT_MAX;
+
+    if (!WriteFile(handle, buffer, len, &bytes_written, NULL)) {
+        _dosmaperr(GetLastError());
+    }
+    n = bytes_written;
+
+#elif defined(MS_WIN64) || defined(MS_WINDOWS)
+    if (len > 32767 && isatty(fd)) {
+        /* Issue #11395: the Windows console returns an error (12: not
+           enough space error) on writing into stdout if stdout mode is
+           binary and the length is greater than 66,000 bytes (or less,
+           depending on heap usage). */
+        len = 32767;
+    }
+    else if (len > INT_MAX)
+        len = INT_MAX;
+    n = write(fd, buffer, (int)len);
+#else
+    n = write(fd, buffer, len);
+#endif
+    return n;
+}
 
 static int
 fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
@@ -398,10 +477,12 @@
     if (dircheck(self, nameobj) < 0)
         goto error;
 
+#ifndef USE_WIN32_READWRITEFILE
 #if defined(MS_WINDOWS) || defined(__CYGWIN__)
     /* don't translate newlines (\r\n <=> \n) */
     _setmode(self->fd, O_BINARY);
 #endif
+#endif
 
     if (PyObject_SetAttrString((PyObject *)self, "name", nameobj) < 0)
         goto error;
@@ -533,13 +614,7 @@
         len = pbuf.len;
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
-#if defined(MS_WIN64) || defined(MS_WINDOWS)
-        if (len > INT_MAX)
-            len = INT_MAX;
-        n = read(self->fd, pbuf.buf, (int)len);
-#else
-        n = read(self->fd, pbuf.buf, len);
-#endif
+        n = internal_read(self->fd, pbuf.buf, len);
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -652,17 +727,7 @@
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
         n = newsize - total;
-#if defined(MS_WIN64) || defined(MS_WINDOWS)
-        if (n > INT_MAX)
-            n = INT_MAX;
-        n = read(self->fd,
-                 PyBytes_AS_STRING(result) + total,
-                 (int)n);
-#else
-        n = read(self->fd,
-                 PyBytes_AS_STRING(result) + total,
-                 n);
-#endif
+        n = internal_read(self->fd, PyBytes_AS_STRING(result) + total, n);
         Py_END_ALLOW_THREADS
         if (n == 0)
             break;
@@ -732,11 +797,7 @@
     if (_PyVerify_fd(self->fd)) {
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
-#if defined(MS_WIN64) || defined(MS_WINDOWS)
-        n = read(self->fd, ptr, (int)size);
-#else
-        n = read(self->fd, ptr, size);
-#endif
+        n = internal_read(self->fd, ptr, size);
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -780,20 +841,7 @@
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
         len = pbuf.len;
-#if defined(MS_WIN64) || defined(MS_WINDOWS)
-        if (len > 32767 && isatty(self->fd)) {
-            /* Issue #11395: the Windows console returns an error (12: not
-               enough space error) on writing into stdout if stdout mode is
-               binary and the length is greater than 66,000 bytes (or less,
-               depending on heap usage). */
-            len = 32767;
-        }
-        else if (len > INT_MAX)
-            len = INT_MAX;
-        n = write(self->fd, pbuf.buf, (int)len);
-#else
-        n = write(self->fd, pbuf.buf, len);
-#endif
+        n = internal_write(self->fd, pbuf.buf, len);
         Py_END_ALLOW_THREADS
     } else
         n = -1;