diff --git a/Lib/UserList.py b/Lib/UserList.py
index 556a327..b445985 100644
--- a/Lib/UserList.py
+++ b/Lib/UserList.py
@@ -25,6 +25,7 @@
         else: return other
     def __cmp__(self, other):
         return cmp(self.data, self.__cast(other))
+    __hash__ = None # Mutable sequence, so not hashable
     def __contains__(self, item): return item in self.data
     def __len__(self): return len(self.data)
     def __getitem__(self, i): return self.data[i]
diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
index 85d733f..a5fee08 100644
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -207,6 +207,9 @@
             other = self._from_iterable(other)
         return (self - other) | (other - self)
 
+    # Sets are not hashable by default, but subclasses can change this
+    __hash__ = None
+
     def _hash(self):
         """Compute the hash value of a set.
 
@@ -350,6 +353,9 @@
     def values(self):
         return [self[key] for key in self]
 
+    # Mappings are not hashable by default, but subclasses can change this
+    __hash__ = None
+
     def __eq__(self, other):
         return isinstance(other, Mapping) and \
                dict(self.items()) == dict(other.items())
diff --git a/Lib/ctypes/test/test_simplesubclasses.py b/Lib/ctypes/test/test_simplesubclasses.py
index 7155170..5671cce 100644
--- a/Lib/ctypes/test/test_simplesubclasses.py
+++ b/Lib/ctypes/test/test_simplesubclasses.py
@@ -6,6 +6,8 @@
         if type(other) != MyInt:
             return -1
         return cmp(self.value, other.value)
+    def __hash__(self): # Silence Py3k warning
+        return hash(self.value)
 
 class Test(unittest.TestCase):
 
diff --git a/Lib/numbers.py b/Lib/numbers.py
index 38240d6..fa59fd8 100644
--- a/Lib/numbers.py
+++ b/Lib/numbers.py
@@ -18,6 +18,9 @@
     """
     __metaclass__ = ABCMeta
 
+    # Concrete numeric types must provide their own hash implementation
+    __hash__ = None
+
 
 ## Notes on Decimal
 ## ----------------
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 70980f8..6671f2c 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1064,6 +1064,7 @@
         class badzero(int):
             def __cmp__(self, other):
                 raise RuntimeError
+            __hash__ = None # Invalid cmp makes this unhashable
         self.assertRaises(RuntimeError, range, a, a + 1, badzero(1))
 
         # Reject floats when it would require PyLongs to represent.
diff --git a/Lib/test/test_coercion.py b/Lib/test/test_coercion.py
index e3a7e43..a70f82d 100644
--- a/Lib/test/test_coercion.py
+++ b/Lib/test/test_coercion.py
@@ -309,6 +309,7 @@
             def __cmp__(slf, other):
                 self.assert_(other == 42, 'expected evil_coercer, got %r' % other)
                 return 0
+            __hash__ = None # Invalid cmp makes this unhashable
         self.assertEquals(cmp(WackyComparer(), evil_coercer), 0)
         # ...and classic classes too, since that code path is a little different
         class ClassicWackyComparer:
diff --git a/Lib/test/test_collections.py b/Lib/test/test_collections.py
index 99eb8cf..d689add 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -172,6 +172,7 @@
         class H(Hashable):
             def __hash__(self):
                 return super(H, self).__hash__()
+            __eq__ = Hashable.__eq__ # Silence Py3k warning
         self.assertEqual(hash(H()), 0)
         self.failIf(issubclass(int, H))
 
diff --git a/Lib/test/test_copy.py b/Lib/test/test_copy.py
index d2899bd..be334cc 100644
--- a/Lib/test/test_copy.py
+++ b/Lib/test/test_copy.py
@@ -435,6 +435,7 @@
                 return (C, (), self.__dict__)
             def __cmp__(self, other):
                 return cmp(self.__dict__, other.__dict__)
+            __hash__ = None # Silence Py3k warning
         x = C()
         x.foo = [42]
         y = copy.copy(x)
@@ -451,6 +452,7 @@
                 self.__dict__.update(state)
             def __cmp__(self, other):
                 return cmp(self.__dict__, other.__dict__)
+            __hash__ = None # Silence Py3k warning
         x = C()
         x.foo = [42]
         y = copy.copy(x)
@@ -477,6 +479,7 @@
             def __cmp__(self, other):
                 return (cmp(list(self), list(other)) or
                         cmp(self.__dict__, other.__dict__))
+            __hash__ = None # Silence Py3k warning
         x = C([[1, 2], 3])
         y = copy.copy(x)
         self.assertEqual(x, y)
@@ -494,6 +497,7 @@
             def __cmp__(self, other):
                 return (cmp(dict(self), list(dict)) or
                         cmp(self.__dict__, other.__dict__))
+            __hash__ = None # Silence Py3k warning
         x = C([("foo", [1, 2]), ("bar", 3)])
         y = copy.copy(x)
         self.assertEqual(x, y)
diff --git a/Lib/test/test_datetime.py b/Lib/test/test_datetime.py
index cdc9eed..1674961 100644
--- a/Lib/test/test_datetime.py
+++ b/Lib/test/test_datetime.py
@@ -986,6 +986,7 @@
                 # compare-by-address (which never says "equal" for distinct
                 # objects).
                 return 0
+            __hash__ = None # Silence Py3k warning
 
         # This still errors, because date and datetime comparison raise
         # TypeError instead of NotImplemented when they don't know what to
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 53b7611..f170d59 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -1121,6 +1121,7 @@
         class G(object):
             def __cmp__(self, other):
                 return 0
+            __hash__ = None # Silence Py3k warning
         g = G()
         orig_objects = len(gc.get_objects())
         for i in xrange(10):
@@ -2727,6 +2728,7 @@
                     if isinstance(other, int) or isinstance(other, long):
                         return cmp(self.value, other)
                     return NotImplemented
+                __hash__ = None # Silence Py3k warning
 
             c1 = C(1)
             c2 = C(2)
@@ -2755,6 +2757,7 @@
                     return abs(self - other) <= 1e-6
                 except:
                     return NotImplemented
+            __hash__ = None # Silence Py3k warning
         zz = ZZ(1.0000003)
         self.assertEqual(zz, 1+0j)
         self.assertEqual(1+0j, zz)
@@ -2767,6 +2770,7 @@
                     self.value = int(value)
                 def __cmp__(self_, other):
                     self.fail("shouldn't call __cmp__")
+                __hash__ = None # Silence Py3k warning
                 def __eq__(self, other):
                     if isinstance(other, C):
                         return self.value == other.value
@@ -3262,6 +3266,7 @@
         class S(str):
             def __eq__(self, other):
                 return self.lower() == other.lower()
+            __hash__ = None # Silence Py3k warning
 
     def test_subclass_propagation(self):
         # Testing propagation of slot functions to subclasses...
diff --git a/Lib/test/test_hash.py b/Lib/test/test_hash.py
index f3954c2..47c66d1 100644
--- a/Lib/test/test_hash.py
+++ b/Lib/test/test_hash.py
@@ -52,6 +52,9 @@
 class OnlyEquality(object):
     def __eq__(self, other):
         return self is other
+    # Trick to suppress Py3k warning in 2.x
+    __hash__ = None
+del OnlyEquality.__hash__
 
 class OnlyInequality(object):
     def __ne__(self, other):
@@ -60,6 +63,9 @@
 class OnlyCmp(object):
     def __cmp__(self, other):
         return cmp(id(self), id(other))
+    # Trick to suppress Py3k warning in 2.x
+    __hash__ = None
+del OnlyCmp.__hash__
 
 class InheritedHashWithEquality(FixedHash, OnlyEquality): pass
 class InheritedHashWithInequality(FixedHash, OnlyInequality): pass
@@ -71,18 +77,15 @@
 class HashInheritanceTestCase(unittest.TestCase):
     default_expected = [object(),
                         DefaultHash(),
+                        OnlyEquality(),
+                        OnlyInequality(),
+                        OnlyCmp(),
                        ]
     fixed_expected = [FixedHash(),
                       InheritedHashWithEquality(),
                       InheritedHashWithInequality(),
                       InheritedHashWithCmp(),
                       ]
-    # TODO: Change these to expecting an exception
-    # when forward porting to Py3k
-    warning_expected = [OnlyEquality(),
-                        OnlyInequality(),
-                        OnlyCmp(),
-                       ]
     error_expected = [NoHash()]
 
     def test_default_hash(self):
@@ -93,20 +96,13 @@
         for obj in self.fixed_expected:
             self.assertEqual(hash(obj), _FIXED_HASH_VALUE)
 
-    def test_warning_hash(self):
-        for obj in self.warning_expected:
-            # TODO: Check for the expected Py3k warning here
-            obj_hash = hash(obj)
-            self.assertEqual(obj_hash, _default_hash(obj))
-
     def test_error_hash(self):
         for obj in self.error_expected:
             self.assertRaises(TypeError, hash, obj)
 
     def test_hashable(self):
         objects = (self.default_expected +
-                   self.fixed_expected +
-                   self.warning_expected)
+                   self.fixed_expected)
         for obj in objects:
             self.assert_(isinstance(obj, Hashable), repr(obj))
 
diff --git a/Lib/test/test_operator.py b/Lib/test/test_operator.py
index 1c3fda3..9bc0a4e 100644
--- a/Lib/test/test_operator.py
+++ b/Lib/test/test_operator.py
@@ -57,6 +57,7 @@
         class C(object):
             def __eq__(self, other):
                 raise SyntaxError
+            __hash__ = None # Silence Py3k warning
         self.failUnlessRaises(TypeError, operator.eq)
         self.failUnlessRaises(SyntaxError, operator.eq, C(), C())
         self.failIf(operator.eq(1, 0))
diff --git a/Lib/test/test_py3kwarn.py b/Lib/test/test_py3kwarn.py
index 67b2538..340e86f 100644
--- a/Lib/test/test_py3kwarn.py
+++ b/Lib/test/test_py3kwarn.py
@@ -12,6 +12,9 @@
 
 class TestPy3KWarnings(unittest.TestCase):
 
+    def assertWarning(self, _, warning, expected_message):
+        self.assertEqual(str(warning.message), expected_message)
+
     def test_backquote(self):
         expected = 'backquote not supported in 3.x; use repr()'
         with catch_warning() as w:
@@ -28,30 +31,41 @@
         with catch_warning() as w:
             safe_exec("True = False")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("False = True")
             self.assertWarning(None, w, expected)
+            w.reset()
             try:
                 safe_exec("obj.False = True")
             except NameError: pass
             self.assertWarning(None, w, expected)
+            w.reset()
             try:
                 safe_exec("obj.True = False")
             except NameError: pass
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("def False(): pass")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("def True(): pass")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("class False: pass")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("class True: pass")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("def f(True=43): pass")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("def f(False=None): pass")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("f(False=True)")
             self.assertWarning(None, w, expected)
+            w.reset()
             safe_exec("f(True=1)")
             self.assertWarning(None, w, expected)
 
@@ -60,20 +74,25 @@
         expected = 'type inequality comparisons not supported in 3.x'
         with catch_warning() as w:
             self.assertWarning(int < str, w, expected)
+            w.reset()
             self.assertWarning(type < object, w, expected)
 
     def test_object_inequality_comparisons(self):
         expected = 'comparing unequal types not supported in 3.x'
         with catch_warning() as w:
             self.assertWarning(str < [], w, expected)
+            w.reset()
             self.assertWarning(object() < (1, 2), w, expected)
 
     def test_dict_inequality_comparisons(self):
         expected = 'dict inequality comparisons not supported in 3.x'
         with catch_warning() as w:
             self.assertWarning({} < {2:3}, w, expected)
+            w.reset()
             self.assertWarning({} <= {}, w, expected)
+            w.reset()
             self.assertWarning({} > {2:3}, w, expected)
+            w.reset()
             self.assertWarning({2:3} >= {}, w, expected)
 
     def test_cell_inequality_comparisons(self):
@@ -86,6 +105,7 @@
         cell1, = f(1).func_closure
         with catch_warning() as w:
             self.assertWarning(cell0 == cell1, w, expected)
+            w.reset()
             self.assertWarning(cell0 < cell1, w, expected)
 
     def test_code_inequality_comparisons(self):
@@ -96,8 +116,11 @@
             pass
         with catch_warning() as w:
             self.assertWarning(f.func_code < g.func_code, w, expected)
+            w.reset()
             self.assertWarning(f.func_code <= g.func_code, w, expected)
+            w.reset()
             self.assertWarning(f.func_code >= g.func_code, w, expected)
+            w.reset()
             self.assertWarning(f.func_code > g.func_code, w, expected)
 
     def test_builtin_function_or_method_comparisons(self):
@@ -107,13 +130,13 @@
         meth = {}.get
         with catch_warning() as w:
             self.assertWarning(func < meth, w, expected)
+            w.reset()
             self.assertWarning(func > meth, w, expected)
+            w.reset()
             self.assertWarning(meth <= func, w, expected)
+            w.reset()
             self.assertWarning(meth >= func, w, expected)
 
-    def assertWarning(self, _, warning, expected_message):
-        self.assertEqual(str(warning.message), expected_message)
-
     def test_sort_cmp_arg(self):
         expected = "the cmp argument is not supported in 3.x"
         lst = range(5)
@@ -121,8 +144,11 @@
 
         with catch_warning() as w:
             self.assertWarning(lst.sort(cmp=cmp), w, expected)
+            w.reset()
             self.assertWarning(sorted(lst, cmp=cmp), w, expected)
+            w.reset()
             self.assertWarning(lst.sort(cmp), w, expected)
+            w.reset()
             self.assertWarning(sorted(lst, cmp), w, expected)
 
     def test_sys_exc_clear(self):
@@ -156,7 +182,7 @@
             self.assertWarning(None, w, expected)
 
     def test_buffer(self):
-        expected = 'buffer() not supported in 3.x; use memoryview()'
+        expected = 'buffer() not supported in 3.x'
         with catch_warning() as w:
             self.assertWarning(buffer('a'), w, expected)
 
@@ -167,6 +193,64 @@
             with catch_warning() as w:
                 self.assertWarning(f.xreadlines(), w, expected)
 
+    def test_hash_inheritance(self):
+        with catch_warning() as w:
+            # With object as the base class
+            class WarnOnlyCmp(object):
+                def __cmp__(self, other): pass
+            self.assertEqual(len(w.warnings), 1)
+            self.assertWarning(None, w,
+                 "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
+            w.reset()
+            class WarnOnlyEq(object):
+                def __eq__(self, other): pass
+            self.assertEqual(len(w.warnings), 1)
+            self.assertWarning(None, w,
+                 "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
+            w.reset()
+            class WarnCmpAndEq(object):
+                def __cmp__(self, other): pass
+                def __eq__(self, other): pass
+            self.assertEqual(len(w.warnings), 2)
+            self.assertWarning(None, w.warnings[-2],
+                 "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
+            self.assertWarning(None, w,
+                 "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
+            w.reset()
+            class NoWarningOnlyHash(object):
+                def __hash__(self): pass
+            self.assertEqual(len(w.warnings), 0)
+            # With an intermediate class in the heirarchy
+            class DefinesAllThree(object):
+                def __cmp__(self, other): pass
+                def __eq__(self, other): pass
+                def __hash__(self): pass
+            class WarnOnlyCmp(DefinesAllThree):
+                def __cmp__(self, other): pass
+            self.assertEqual(len(w.warnings), 1)
+            self.assertWarning(None, w,
+                 "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
+            w.reset()
+            class WarnOnlyEq(DefinesAllThree):
+                def __eq__(self, other): pass
+            self.assertEqual(len(w.warnings), 1)
+            self.assertWarning(None, w,
+                 "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
+            w.reset()
+            class WarnCmpAndEq(DefinesAllThree):
+                def __cmp__(self, other): pass
+                def __eq__(self, other): pass
+            self.assertEqual(len(w.warnings), 2)
+            self.assertWarning(None, w.warnings[-2],
+                 "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
+            self.assertWarning(None, w,
+                 "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
+            w.reset()
+            class NoWarningOnlyHash(DefinesAllThree):
+                def __hash__(self): pass
+            self.assertEqual(len(w.warnings), 0)
+
+
 
 class TestStdlibRemovals(unittest.TestCase):
 
diff --git a/Lib/test/test_slice.py b/Lib/test/test_slice.py
index 8c90c10..854805b 100644
--- a/Lib/test/test_slice.py
+++ b/Lib/test/test_slice.py
@@ -33,6 +33,7 @@
         class BadCmp(object):
             def __eq__(self, other):
                 raise Exc
+            __hash__ = None # Silence Py3k warning
 
         s1 = slice(BadCmp())
         s2 = slice(BadCmp())
diff --git a/Lib/test/test_sort.py b/Lib/test/test_sort.py
index 84c92cc..a61fb96 100644
--- a/Lib/test/test_sort.py
+++ b/Lib/test/test_sort.py
@@ -70,6 +70,7 @@
 
             def __cmp__(self, other):
                 return cmp(self.key, other.key)
+            __hash__ = None # Silence Py3k warning
 
             def __repr__(self):
                 return "Stable(%d, %d)" % (self.key, self.index)
diff --git a/Lib/unittest.py b/Lib/unittest.py
index b5a1a4b..09c6ca9 100644
--- a/Lib/unittest.py
+++ b/Lib/unittest.py
@@ -425,6 +425,9 @@
     def __ne__(self, other):
         return not self == other
 
+    # Can't guarantee hash invariant, so flag as unhashable
+    __hash__ = None
+
     def __iter__(self):
         return iter(self._tests)
 
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index 9f7f62c..ad42947 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -516,6 +516,7 @@
 
     __len__ = _get_length
 
+    __hash__ = None # Mutable type can't be correctly hashed
     def __cmp__(self, other):
         if self._attrs is getattr(other, "_attrs", None):
             return 0
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 0af3f30..42974f8 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -3648,6 +3648,22 @@
 		type->tp_flags |= Py_TPFLAGS_DICT_SUBCLASS;
 }
 
+static int
+overrides_name(PyTypeObject *type, char *name)
+{
+	PyObject *dict = type->tp_dict;
+
+	assert(dict != NULL);
+	if (PyDict_GetItemString(dict, name) != NULL) {
+		return 1;
+	}
+	return 0;
+}
+
+#define OVERRIDES_HASH(x)       overrides_name(x, "__hash__")
+#define OVERRIDES_CMP(x)        overrides_name(x, "__cmp__")
+#define OVERRIDES_EQ(x)         overrides_name(x, "__eq__")
+
 static void
 inherit_slots(PyTypeObject *type, PyTypeObject *base)
 {
@@ -3786,6 +3802,25 @@
 			type->tp_compare = base->tp_compare;
 			type->tp_richcompare = base->tp_richcompare;
 			type->tp_hash = base->tp_hash;
+			/* Check for changes to inherited methods in Py3k*/
+			if (Py_Py3kWarningFlag) {
+				if (base->tp_hash &&
+						(base->tp_hash != PyObject_HashNotImplemented) &&
+						!OVERRIDES_HASH(type)) {
+					if (OVERRIDES_CMP(type)) {
+						PyErr_WarnPy3k("Overriding "
+						  "__cmp__ blocks inheritance "
+						  "of __hash__ in 3.x",
+						  1);
+					}
+					if (OVERRIDES_EQ(type)) {
+						PyErr_WarnPy3k("Overriding "
+						  "__eq__ blocks inheritance "
+						  "of __hash__ in 3.x",
+						  1);
+					}
+				}
+			}
 		}
 	}
 	else {