diff --git a/Lib/email/quoprimime.py b/Lib/email/quoprimime.py
index 168dfffa478..bffad4efa32 100644
--- a/Lib/email/quoprimime.py
+++ b/Lib/email/quoprimime.py
@@ -135,9 +135,9 @@ def header_encode(header_bytes, charset='iso-8859-1'):
     charset names the character set to use in the RFC 2046 header.  It
     defaults to iso-8859-1.
     """
-    # Return empty headers unchanged
+    # Return empty headers as an empty string.
     if not header_bytes:
-        return str(header_bytes)
+        return ''
     # Iterate over every byte, encoding if necessary.
     encoded = []
     for octet in header_bytes:
@@ -268,7 +268,7 @@ def decode(encoded, eol=NL):
             if i == n:
                 decoded += eol
     # Special case if original string did not end with eol
-    if not encoded.endswith(eol) and decoded.endswith(eol):
+    if encoded[-1] not in '\r\n' and decoded.endswith(eol):
         decoded = decoded[:-1]
     return decoded
 
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 1e72f800b9d..a00f15aae4b 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -374,6 +374,13 @@ def main(tests=None, testdir=None, verbose=0, quiet=False,
             forever = True
         elif o in ('-j', '--multiprocess'):
             use_mp = int(a)
+            if use_mp <= 0:
+                try:
+                    import multiprocessing
+                    # Use all cores + extras for tests that like to sleep
+                    use_mp = 2 + multiprocessing.cpu_count()
+                except (ImportError, NotImplementedError):
+                    use_mp = 3
         elif o == '--header':
             header = True
         elif o == '--slaveargs':
diff --git a/Lib/test/support.py b/Lib/test/support.py
index 66d7f934370..52ec2320db0 100644
--- a/Lib/test/support.py
+++ b/Lib/test/support.py
@@ -1389,9 +1389,8 @@ def args_from_interpreter_flags():
         v = getattr(sys.flags, flag)
         if v > 0:
             args.append('-' + opt * v)
-        if sys.warnoptions:
-            args.append('-W')
-            args.extend(sys.warnoptions)
+    for opt in sys.warnoptions:
+        args.append('-W' + opt)
     return args
 
 #============================================================
diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index 29dd0fc7ab2..bc6a309861c 100644
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -3344,21 +3344,200 @@ class TestQuopri(unittest.TestCase):
             c = chr(x)
             self.assertEqual(quoprimime.unquote(quoprimime.quote(c)), c)
 
-    def test_header_encode(self):
-        eq = self.assertEqual
-        he = quoprimime.header_encode
-        eq(he(b'hello'), '=?iso-8859-1?q?hello?=')
-        eq(he(b'hello', charset='iso-8859-2'), '=?iso-8859-2?q?hello?=')
-        eq(he(b'hello\nworld'), '=?iso-8859-1?q?hello=0Aworld?=')
-        # Test a non-ASCII character
-        eq(he(b'hello\xc7there'), '=?iso-8859-1?q?hello=C7there?=')
+    def _test_header_encode(self, header, expected_encoded_header, charset=None):
+        if charset is None:
+            encoded_header = quoprimime.header_encode(header)
+        else:
+            encoded_header = quoprimime.header_encode(header, charset)
+        self.assertEqual(encoded_header, expected_encoded_header)
 
-    def test_decode(self):
-        eq = self.assertEqual
-        eq(quoprimime.decode(''), '')
-        eq(quoprimime.decode('hello'), 'hello')
-        eq(quoprimime.decode('hello', 'X'), 'hello')
-        eq(quoprimime.decode('hello\nworld', 'X'), 'helloXworld')
+    def test_header_encode_null(self):
+        self._test_header_encode(b'', '')
+
+    def test_header_encode_one_word(self):
+        self._test_header_encode(b'hello', '=?iso-8859-1?q?hello?=')
+
+    def test_header_encode_two_lines(self):
+        self._test_header_encode(b'hello\nworld',
+                                '=?iso-8859-1?q?hello=0Aworld?=')
+
+    def test_header_encode_non_ascii(self):
+        self._test_header_encode(b'hello\xc7there',
+                                '=?iso-8859-1?q?hello=C7there?=')
+
+    def test_header_encode_alt_charset(self):
+        self._test_header_encode(b'hello', '=?iso-8859-2?q?hello?=',
+                charset='iso-8859-2')
+
+    def _test_header_decode(self, encoded_header, expected_decoded_header):
+        decoded_header = quoprimime.header_decode(encoded_header)
+        self.assertEqual(decoded_header, expected_decoded_header)
+
+    def test_header_decode_null(self):
+        self._test_header_decode('', '')
+
+    def test_header_decode_one_word(self):
+        self._test_header_decode('hello', 'hello')
+
+    def test_header_decode_two_lines(self):
+        self._test_header_decode('hello=0Aworld', 'hello\nworld')
+
+    def test_header_decode_non_ascii(self):
+        self._test_header_decode('hello=C7there', 'hello\xc7there')
+
+    def _test_decode(self, encoded, expected_decoded, eol=None):
+        if eol is None:
+            decoded = quoprimime.decode(encoded)
+        else:
+            decoded = quoprimime.decode(encoded, eol=eol)
+        self.assertEqual(decoded, expected_decoded)
+
+    def test_decode_null_word(self):
+        self._test_decode('', '')
+
+    def test_decode_null_line_null_word(self):
+        self._test_decode('\r\n', '\n')
+
+    def test_decode_one_word(self):
+        self._test_decode('hello', 'hello')
+
+    def test_decode_one_word_eol(self):
+        self._test_decode('hello', 'hello', eol='X')
+
+    def test_decode_one_line(self):
+        self._test_decode('hello\r\n', 'hello\n')
+
+    def test_decode_one_line_lf(self):
+        self._test_decode('hello\n', 'hello\n')
+
+    def test_decode_one_line_cr(self):
+        self._test_decode('hello\r', 'hello\n')
+
+    def test_decode_one_line_nl(self):
+        self._test_decode('hello\n', 'helloX', eol='X')
+
+    def test_decode_one_line_crnl(self):
+        self._test_decode('hello\r\n', 'helloX', eol='X')
+
+    def test_decode_one_line_one_word(self):
+        self._test_decode('hello\r\nworld', 'hello\nworld')
+
+    def test_decode_one_line_one_word_eol(self):
+        self._test_decode('hello\r\nworld', 'helloXworld', eol='X')
+
+    def test_decode_two_lines(self):
+        self._test_decode('hello\r\nworld\r\n', 'hello\nworld\n')
+
+    def test_decode_two_lines_eol(self):
+        self._test_decode('hello\r\nworld\r\n', 'helloXworldX', eol='X')
+
+    def test_decode_one_long_line(self):
+        self._test_decode('Spam' * 250, 'Spam' * 250)
+
+    def test_decode_one_space(self):
+        self._test_decode(' ', '')
+
+    def test_decode_multiple_spaces(self):
+        self._test_decode(' ' * 5, '')
+
+    def test_decode_one_line_trailing_spaces(self):
+        self._test_decode('hello    \r\n', 'hello\n')
+
+    def test_decode_two_lines_trailing_spaces(self):
+        self._test_decode('hello    \r\nworld   \r\n', 'hello\nworld\n')
+
+    def test_decode_quoted_word(self):
+        self._test_decode('=22quoted=20words=22', '"quoted words"')
+
+    def test_decode_uppercase_quoting(self):
+        self._test_decode('ab=CD=EF', 'ab\xcd\xef')
+
+    def test_decode_lowercase_quoting(self):
+        self._test_decode('ab=cd=ef', 'ab\xcd\xef')
+
+    def test_decode_soft_line_break(self):
+        self._test_decode('soft line=\r\nbreak', 'soft linebreak')
+
+    def test_decode_false_quoting(self):
+        self._test_decode('A=1,B=A ==> A+B==2', 'A=1,B=A ==> A+B==2')
+
+    def _test_encode(self, body, expected_encoded_body, maxlinelen=None, eol=None):
+        kwargs = {}
+        if maxlinelen is None:
+            # Use body_encode's default.
+            maxlinelen = 76
+        else:
+            kwargs['maxlinelen'] = maxlinelen
+        if eol is None:
+            # Use body_encode's default.
+            eol = '\n'
+        else:
+            kwargs['eol'] = eol
+        encoded_body = quoprimime.body_encode(body, **kwargs)
+        self.assertEqual(encoded_body, expected_encoded_body)
+        if eol == '\n' or eol == '\r\n':
+            # We know how to split the result back into lines, so maxlinelen
+            # can be checked.
+            for line in encoded_body.splitlines():
+                self.assertLessEqual(len(line), maxlinelen)
+
+    def test_encode_null(self):
+        self._test_encode('', '')
+
+    def test_encode_null_lines(self):
+        self._test_encode('\n\n', '\n\n')
+
+    def test_encode_one_line(self):
+        self._test_encode('hello\n', 'hello\n')
+
+    def test_encode_one_line_crlf(self):
+        self._test_encode('hello\r\n', 'hello\n')
+
+    def test_encode_one_line_eol(self):
+        self._test_encode('hello\n', 'hello\r\n', eol='\r\n')
+
+    def test_encode_one_space(self):
+        self._test_encode(' ', '=20')
+
+    def test_encode_one_line_one_space(self):
+        self._test_encode(' \n', '=20\n')
+
+    def test_encode_one_word_trailing_spaces(self):
+        self._test_encode('hello   ', 'hello  =20')
+
+    def test_encode_one_line_trailing_spaces(self):
+        self._test_encode('hello   \n', 'hello  =20\n')
+
+    def test_encode_one_word_trailing_tab(self):
+        self._test_encode('hello  \t', 'hello  =09')
+
+    def test_encode_one_line_trailing_tab(self):
+        self._test_encode('hello  \t\n', 'hello  =09\n')
+
+    def test_encode_trailing_space_before_maxlinelen(self):
+        self._test_encode('abcd \n1234', 'abcd =\n\n1234', maxlinelen=6)
+
+    def test_encode_trailing_space_beyond_maxlinelen(self):
+        self._test_encode('abcd \n1234', 'abc=\nd =\n\n1234', maxlinelen=4)
+
+    def test_encode_quoted_equals(self):
+        self._test_encode('a = b', 'a =3D b')
+
+    def test_encode_one_long_string(self):
+        self._test_encode('x' * 100, 'x' * 75 + '=\n' + 'x' * 25)
+
+    def test_encode_one_long_line(self):
+        self._test_encode('x' * 100 + '\n', 'x' * 75 + '=\n' + 'x' * 25 + '\n')
+
+    def test_encode_one_very_long_line(self):
+        self._test_encode('x' * 200 + '\n',
+                2 * ('x' * 75 + '=\n') + 'x' * 50 + '\n')
+
+    def test_encode_one_long_line(self):
+        self._test_encode('x' * 100 + '\n', 'x' * 75 + '=\n' + 'x' * 25 + '\n')
+
+    def test_encode_shortest_maxlinelen(self):
+        self._test_encode('=' * 5, '=3D=\n' * 4 + '=3D', maxlinelen=4)
 
     def test_encode(self):
         eq = self.assertEqual
diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
index f73565eb46f..78de90923ec 100644
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -3,6 +3,7 @@ import re
 import sys
 from io import StringIO
 import unittest
+from math import copysign
 
 def disassemble(func):
     f = StringIO()
@@ -207,6 +208,9 @@ class TestTranforms(unittest.TestCase):
     def test_folding_of_unaryops_on_constants(self):
         for line, elem in (
             ('-0.5', '(-0.5)'),                     # unary negative
+            ('-0.0', '(-0.0)'),                     # -0.0
+            ('-(1.0-1.0)','(-0.0)'),                # -0.0 after folding
+            ('-0', '(0)'),                          # -0
             ('~-2', '(1)'),                         # unary invert
             ('+1', '(1)'),                          # unary positive
         ):
@@ -214,6 +218,13 @@ class TestTranforms(unittest.TestCase):
             self.assertIn(elem, asm, asm)
             self.assertNotIn('UNARY_', asm)
 
+        # Check that -0.0 works after marshaling
+        def negzero():
+            return -(1.0-1.0)
+
+        self.assertNotIn('UNARY_', disassemble(negzero))
+        self.assertTrue(copysign(1.0, negzero()) < 0)
+
         # Verify that unfoldables are skipped
         for line, elem in (
             ('-"abc"', "('abc')"),                  # unary negative
diff --git a/Misc/ACKS b/Misc/ACKS
index 91bcec8ebbf..58011519d9d 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -867,6 +867,7 @@ Christian Tismer
 Frank J. Tobin
 R Lindsay Todd
 Bennett Todd
+Eugene Toder
 Matias Torchinsky
 Sandro Tosi
 Richard Townsend
diff --git a/Misc/NEWS b/Misc/NEWS
index 363d5e99b34..64a35ddf58b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@ What's New in Python 3.3 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #11244: Remove an unnecessary peepholer check that was preventing
+  negative zeros from being constant-folded properly.
+
 - Issue #11395: io.FileIO().write() clamps the data length to 32,767 bytes on
   Windows if the file is a TTY to workaround a Windows bug. The Windows console
   returns an error (12: not enough space error) on writing into stdout if
diff --git a/Python/peephole.c b/Python/peephole.c
index 4bc65dcc312..69f61617f87 100644
--- a/Python/peephole.c
+++ b/Python/peephole.c
@@ -238,7 +238,7 @@ fold_binops_on_constants(unsigned char *codestr, PyObject *consts, PyObject **ob
 static int
 fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts, PyObject *v)
 {
-    PyObject *newconst=NULL/*, *v*/;
+    PyObject *newconst;
     Py_ssize_t len_consts;
     int opcode;
 
@@ -250,9 +250,7 @@ fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts, PyObject *v
     opcode = codestr[3];
     switch (opcode) {
         case UNARY_NEGATIVE:
-            /* Preserve the sign of -0.0 */
-            if (PyObject_IsTrue(v) == 1)
-                newconst = PyNumber_Negative(v);
+            newconst = PyNumber_Negative(v);
             break;
         case UNARY_INVERT:
             newconst = PyNumber_Invert(v);