diff --git a/.hgignore b/.hgignore
index d3983dcf2ea..70aca549360 100644
--- a/.hgignore
+++ b/.hgignore
@@ -50,6 +50,7 @@ libpython*.a
 *~
 Lib/lib2to3/*.pickle
 Lib/test/data/*
+Misc/*.wpu
 PC/python_nt*.h
 PC/pythonnt_rc*.h
 PC/*.obj
diff --git a/Doc/library/email.message.rst b/Doc/library/email.message.rst
index ebe2d9cb476..1e6a4853537 100644
--- a/Doc/library/email.message.rst
+++ b/Doc/library/email.message.rst
@@ -139,15 +139,22 @@ Here are the methods of the :class:`Message` class:
       string naming a character set, or ``None``.  If it is a string, it will
       be converted to a :class:`~email.charset.Charset` instance.  If *charset*
       is ``None``, the ``charset`` parameter will be removed from the
-      :mailheader:`Content-Type` header. Anything else will generate a
-      :exc:`TypeError`.
+      :mailheader:`Content-Type` header (the message will not be otherwise
+      modified).  Anything else will generate a :exc:`TypeError`.
 
-      The message will be assumed to be of type :mimetype:`text/\*` encoded with
-      *charset.input_charset*.  It will be converted to *charset.output_charset*
-      and encoded properly, if needed, when generating the plain text
-      representation of the message.  MIME headers (:mailheader:`MIME-Version`,
-      :mailheader:`Content-Type`, :mailheader:`Content-Transfer-Encoding`) will
-      be added as needed.
+      If there is no existing :mailheader:`MIME-Version` header one will be
+      added.  If there is no existing :mailheader:`Content-Type` header, one
+      will be added with a value of :mimetype:`text/plain`.  Whether the
+      :mailheader:`Content-Type` header already exists or not, its ``charset``
+      parameter will be set to *charset.output_charset*.   If
+      *charset.input_charset* and *charset.output_charset* differ, the payload
+      will be re-encoded to the *output_charset*.  If there is no existing
+      :mailheader:`Content-Transfer-Encoding` header, then the payload will be
+      transfer-encoded, if needed, using the specified
+      :class:`~email.charset.Charset`, and a header with the appropriate value
+      will be added.  If a :mailheader:`Content-Transfer-Encoding` header
+      already exists, the payload is assumed to already be correctly encoded
+      using that :mailheader:`Content-Transfer-Encoding` and is not modified.
 
    .. method:: get_charset()
 
diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
index a9eb23fde31..f73565eb46f 100644
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -19,6 +19,7 @@ def disassemble(func):
 def dis_single(line):
     return disassemble(compile(line, '', 'single'))
 
+
 class TestTranforms(unittest.TestCase):
 
     def test_unot(self):
@@ -294,11 +295,23 @@ class TestTranforms(unittest.TestCase):
             self.assertNotIn('BINARY_', asm, e)
             self.assertNotIn('BUILD_', asm, e)
 
+class TestBuglets(unittest.TestCase):
+
+    def test_bug_11510(self):
+        # folded constant set optimization was commingled with the tuple
+        # unpacking optimization which would fail if the set had duplicate
+        # elements so that the set length was unexpected
+        def f():
+            x, y = {1, 1}
+            return x, y
+        with self.assertRaises(ValueError):
+            f()
+
 
 def test_main(verbose=None):
     import sys
     from test import support
-    test_classes = (TestTranforms,)
+    test_classes = (TestTranforms, TestBuglets)
     support.run_unittest(*test_classes)
 
     # verify reference counting
diff --git a/Misc/python-wing4.wpr b/Misc/python-wing4.wpr
index 795b694150c..7adfdbdacf7 100644
--- a/Misc/python-wing4.wpr
+++ b/Misc/python-wing4.wpr
@@ -5,11 +5,12 @@
 ##################################################################
 [project attributes]
 proj.directory-list = [{'dirloc': loc('..'),
-                        'excludes': [u'Lib/unittest/test/__pycache__',
-                                     u'Lib/__pycache__',
-                                     u'Doc/build',
+                        'excludes': [u'.hg',
                                      u'Lib/unittest/__pycache__',
-                                     u'build'],
+                                     u'Lib/unittest/test/__pycache__',
+                                     u'Lib/__pycache__',
+                                     u'build',
+                                     u'Doc/build'],
                         'filter': '*',
                         'include_hidden': False,
                         'recursive': True,
diff --git a/Python/peephole.c b/Python/peephole.c
index ab96ce9def2..4bc65dcc312 100644
--- a/Python/peephole.c
+++ b/Python/peephole.c
@@ -535,7 +535,8 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
                 }
                 if (codestr[i+3] != UNPACK_SEQUENCE  ||
                     !ISBASICBLOCK(blocks,i,6) ||
-                    j != GETARG(codestr, i+3))
+                    j != GETARG(codestr, i+3) ||
+                    opcode == BUILD_SET)
                     continue;
                 if (j == 1) {
                     memset(codestr+i, NOP, 6);