diff -r d758c5965199 Lib/tempfile.py
--- a/Lib/tempfile.py	Sun Apr 10 18:12:01 2016 +0300
+++ b/Lib/tempfile.py	Sun Apr 10 23:36:13 2016 +0300
@@ -639,10 +639,9 @@ class SpooledTemporaryFile:
         if 'b' in mode:
             self._file = _io.BytesIO()
         else:
-            # Setting newline="\n" avoids newline translation;
-            # this is important because otherwise on Windows we'd
-            # get double newline translation upon rollover().
-            self._file = _io.StringIO(newline="\n")
+            self._file = _io.TextIOWrapper(_io.BytesIO(),
+                            encoding=encoding, newline=newline,
+                            write_through=True)
         self._max_size = max_size
         self._rolled = False
         self._TemporaryFileArgs = {'mode': mode, 'buffering': buffering,
@@ -662,8 +661,12 @@ class SpooledTemporaryFile:
         newfile = self._file = TemporaryFile(**self._TemporaryFileArgs)
         del self._TemporaryFileArgs
 
-        newfile.write(file.getvalue())
-        newfile.seek(file.tell(), 0)
+        pos = file.tell()
+        if hasattr(newfile, 'buffer'):
+            newfile.buffer.write(file.detach().getvalue())
+        else:
+            newfile.write(file.getvalue())
+        newfile.seek(pos, 0)
 
         self._rolled = True
 
diff -r d758c5965199 Lib/test/test_tempfile.py
--- a/Lib/test/test_tempfile.py	Sun Apr 10 18:12:01 2016 +0300
+++ b/Lib/test/test_tempfile.py	Sun Apr 10 23:36:13 2016 +0300
@@ -1112,8 +1112,8 @@ class TestSpooledTemporaryFile(BaseTestC
         self.assertFalse(f._rolled)
         self.assertEqual(f.mode, 'w+')
         self.assertIsNone(f.name)
-        self.assertIsNone(f.newlines)
-        self.assertIsNone(f.encoding)
+        self.assertEqual(f.newlines, os.linesep)
+        self.assertIsNotNone(f.encoding)
 
         f.write("xyzzy\n")
         f.seek(0)
@@ -1137,12 +1137,14 @@ class TestSpooledTemporaryFile(BaseTestC
         self.assertFalse(f._rolled)
         self.assertEqual(f.mode, 'w+')
         self.assertIsNone(f.name)
-        self.assertIsNone(f.newlines)
-        self.assertIsNone(f.encoding)
+        self.assertIsNotNone(f.newlines)
+        self.assertEqual(f.encoding, 'utf-8')
 
-        f.write("\u039B" * 20 + "\r\n")
+        f.write("\u039C" * 10 + "\r\n")
+        f.write("\u039D" * 20)
         f.seek(0)
-        self.assertEqual(f.read(), "\u039B\r\n" + ("\u039B" * 20) + "\r\n")
+        self.assertEqual(f.read(),
+                "\u039B\r\n" + ("\u039C" * 10) + "\r\n" + ("\u039D" * 20))
         self.assertTrue(f._rolled)
         self.assertEqual(f.mode, 'w+')
         self.assertIsNotNone(f.name)