diff -r 0238eafb68da Lib/test/test_sys.py
--- a/Lib/test/test_sys.py	Wed Oct 14 18:25:31 2015 +0200
+++ b/Lib/test/test_sys.py	Fri Oct 16 19:26:14 2015 +0300
@@ -1112,6 +1112,26 @@ class SizeofTest(unittest.TestCase):
         # weakcallableproxy
         check(weakref.proxy(int), size('2Pn2P'))
 
+    def check_slots(self, obj, base, extra):
+        self.assertEqual(sys.getsizeof(obj),
+                         sys.getsizeof(base) + struct.calcsize(extra))
+    def test_slots(self):
+        # check all subclassable types defined in Objects/ that allow
+        # non-empty __slots__
+        check = self.check_slots
+        class BA(bytearray):
+            __slots__ = 'a', 'b', 'c'
+        check(BA(), bytearray(), '3P3P')
+        class D(dict):
+            __slots__ = 'a', 'b', 'c'
+        check(D(), {}, '3P')
+        class L(list):
+            __slots__ = 'a', 'b', 'c'
+        check(L(), [], '3P')
+        class S(set):
+            __slots__ = 'a', 'b', 'c'
+        check(S(), set(), '3P')
+
     def test_pythontypes(self):
         # check all types defined in Python/
         size = test.support.calcobjsize
diff -r 0238eafb68da Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_collectionsmodule.c	Fri Oct 16 19:26:14 2015 +0300
@@ -1479,7 +1479,7 @@ deque_sizeof(dequeobject *deque, void *u
     Py_ssize_t res;
     Py_ssize_t blocks;
 
-    res = sizeof(dequeobject);
+    res = _PyObject_SIZE(Py_TYPE(deque));
     blocks = (deque->leftindex + Py_SIZE(deque) + BLOCKLEN - 1) / BLOCKLEN;
     assert(deque->leftindex + Py_SIZE(deque) - 1 ==
            (blocks - 1) * BLOCKLEN + deque->rightindex);
diff -r 0238eafb68da Modules/_decimal/_decimal.c
--- a/Modules/_decimal/_decimal.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_decimal/_decimal.c	Fri Oct 16 19:26:14 2015 +0300
@@ -4529,7 +4529,7 @@ dec_sizeof(PyObject *v, PyObject *dummy 
 {
     Py_ssize_t res;
 
-    res = sizeof(PyDecObject);
+    res = _PyObject_SIZE(Py_TYPE(v));
     if (mpd_isdynamic_data(MPD(v))) {
         res += MPD(v)->alloc * sizeof(mpd_uint_t);
     }
diff -r 0238eafb68da Modules/_elementtree.c
--- a/Modules/_elementtree.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_elementtree.c	Fri Oct 16 19:26:14 2015 +0300
@@ -847,7 +847,7 @@ static Py_ssize_t
 _elementtree_Element___sizeof___impl(ElementObject *self)
 /*[clinic end generated code: output=bf73867721008000 input=70f4b323d55a17c1]*/
 {
-    Py_ssize_t result = sizeof(ElementObject);
+    Py_ssize_t result = _PyObject_SIZE(Py_TYPE(self));
     if (self->extra) {
         result += sizeof(ElementObjectExtra);
         if (self->extra->children != self->extra->_children)
diff -r 0238eafb68da Modules/_io/bufferedio.c
--- a/Modules/_io/bufferedio.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_io/bufferedio.c	Fri Oct 16 19:26:14 2015 +0300
@@ -423,7 +423,7 @@ buffered_sizeof(buffered *self, void *un
 {
     Py_ssize_t res;
 
-    res = sizeof(buffered);
+    res = _PyObject_SIZE(Py_TYPE(self));
     if (self->buffer)
         res += self->buffer_size;
     return PyLong_FromSsize_t(res);
diff -r 0238eafb68da Modules/_io/bytesio.c
--- a/Modules/_io/bytesio.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_io/bytesio.c	Fri Oct 16 19:26:14 2015 +0300
@@ -991,7 +991,7 @@ bytesio_sizeof(bytesio *self, void *unus
 {
     Py_ssize_t res;
 
-    res = sizeof(bytesio);
+    res = _PyObject_SIZE(Py_TYPE(self));
     if (self->buf && !SHARED_BUF(self))
         res += _PySys_GetSizeOf(self->buf);
     return PyLong_FromSsize_t(res);
diff -r 0238eafb68da Modules/_pickle.c
--- a/Modules/_pickle.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_pickle.c	Fri Oct 16 19:26:14 2015 +0300
@@ -4077,7 +4077,7 @@ static Py_ssize_t
 {
     Py_ssize_t res, s;
 
-    res = sizeof(PicklerObject);
+    res = _PyObject_SIZE(Py_TYPE(self));
     if (self->memo != NULL) {
         res += sizeof(PyMemoTable);
         res += self->memo->mt_allocated * sizeof(PyMemoEntry);
@@ -6476,7 +6476,7 @@ static Py_ssize_t
 {
     Py_ssize_t res;
 
-    res = sizeof(UnpicklerObject);
+    res = _PyObject_SIZE(Py_TYPE(self));
     if (self->memo != NULL)
         res += self->memo_size * sizeof(PyObject *);
     if (self->marks != NULL)
diff -r 0238eafb68da Modules/_struct.c
--- a/Modules/_struct.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/_struct.c	Fri Oct 16 19:26:14 2015 +0300
@@ -1924,7 +1924,7 @@ s_sizeof(PyStructObject *self, void *unu
     Py_ssize_t size;
     formatcode *code;
 
-    size = sizeof(PyStructObject) + sizeof(formatcode);
+    size = _PyObject_SIZE(Py_TYPE(self)) + sizeof(formatcode);
     for (code = self->s_codes; code->fmtdef != NULL; code++)
         size += sizeof(formatcode);
     return PyLong_FromSsize_t(size);
diff -r 0238eafb68da Modules/arraymodule.c
--- a/Modules/arraymodule.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/arraymodule.c	Fri Oct 16 19:26:14 2015 +0300
@@ -1743,7 +1743,7 @@ array_array___sizeof___impl(arrayobject 
 /*[clinic end generated code: output=d8e1c61ebbe3eaed input=805586565bf2b3c6]*/
 {
     Py_ssize_t res;
-    res = sizeof(arrayobject) + self->allocated * self->ob_descr->itemsize;
+    res = _PyObject_SIZE(Py_TYPE(self)) + self->allocated * self->ob_descr->itemsize;
     return PyLong_FromSsize_t(res);
 }
 
diff -r 0238eafb68da Modules/itertoolsmodule.c
--- a/Modules/itertoolsmodule.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/itertoolsmodule.c	Fri Oct 16 19:26:14 2015 +0300
@@ -2109,7 +2109,7 @@ product_sizeof(productobject *lz, void *
 {
     Py_ssize_t res;
 
-    res = sizeof(productobject);
+    res = _PyObject_SIZE(Py_TYPE(lz));
     res += PyTuple_GET_SIZE(lz->pools) * sizeof(Py_ssize_t);
     return PyLong_FromSsize_t(res);
 }
@@ -2440,7 +2440,7 @@ combinations_sizeof(combinationsobject *
 {
     Py_ssize_t res;
 
-    res = sizeof(combinationsobject);
+    res = _PyObject_SIZE(Py_TYPE(co));
     res += co->r * sizeof(Py_ssize_t);
     return PyLong_FromSsize_t(res);
 }
@@ -2781,7 +2781,7 @@ cwr_sizeof(cwrobject *co, void *unused)
 {
     Py_ssize_t res;
 
-    res = sizeof(cwrobject);
+    res = _PyObject_SIZE(Py_TYPE(co));
     res += co->r * sizeof(Py_ssize_t);
     return PyLong_FromSsize_t(res);
 }
@@ -3129,7 +3129,7 @@ permutations_sizeof(permutationsobject *
 {
     Py_ssize_t res;
 
-    res = sizeof(permutationsobject);
+    res = _PyObject_SIZE(Py_TYPE(po));
     res += PyTuple_GET_SIZE(po->pool) * sizeof(Py_ssize_t);
     res += po->r * sizeof(Py_ssize_t);
     return PyLong_FromSsize_t(res);
diff -r 0238eafb68da Modules/mmapmodule.c
--- a/Modules/mmapmodule.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/mmapmodule.c	Fri Oct 16 19:26:14 2015 +0300
@@ -719,7 +719,7 @@ mmap__sizeof__method(mmap_object *self, 
 {
     Py_ssize_t res;
 
-    res = sizeof(mmap_object);
+    res = _PyObject_SIZE(Py_TYPE(self));
     if (self->tagname)
         res += strlen(self->tagname) + 1;
     return PyLong_FromSsize_t(res);
diff -r 0238eafb68da Modules/parsermodule.c
--- a/Modules/parsermodule.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Modules/parsermodule.c	Fri Oct 16 19:26:14 2015 +0300
@@ -397,7 +397,7 @@ parser_sizeof(PyST_Object *st, void *unu
 {
     Py_ssize_t res;
 
-    res = sizeof(PyST_Object) + _PyNode_SizeOf(st->st_node);
+    res = _PyObject_SIZE(Py_TYPE(st)) + _PyNode_SizeOf(st->st_node);
     return PyLong_FromSsize_t(res);
 }
 
diff -r 0238eafb68da Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Objects/bytearrayobject.c	Fri Oct 16 19:26:14 2015 +0300
@@ -2905,7 +2905,7 @@ bytearray_sizeof_impl(PyByteArrayObject 
 {
     Py_ssize_t res;
 
-    res = sizeof(PyByteArrayObject) + self->ob_alloc * sizeof(char);
+    res = _PyObject_SIZE(Py_TYPE(self)) + self->ob_alloc * sizeof(char);
     return PyLong_FromSsize_t(res);
 }
 
diff -r 0238eafb68da Objects/codeobject.c
--- a/Objects/codeobject.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Objects/codeobject.c	Fri Oct 16 19:26:14 2015 +0300
@@ -384,7 +384,7 @@ code_sizeof(PyCodeObject *co, void *unus
 {
     Py_ssize_t res;
 
-    res = sizeof(PyCodeObject);
+    res = _PyObject_SIZE(Py_TYPE(co));
     if (co->co_cell2arg != NULL && co->co_cellvars != NULL)
         res += PyTuple_GET_SIZE(co->co_cellvars) * sizeof(unsigned char);
     return PyLong_FromSsize_t(res);
diff -r 0238eafb68da Objects/dictobject.c
--- a/Objects/dictobject.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Objects/dictobject.c	Fri Oct 16 19:26:14 2015 +0300
@@ -2560,7 +2560,7 @@ PyObject *
     Py_ssize_t size, res;
 
     size = DK_SIZE(mp->ma_keys);
-    res = sizeof(PyDictObject);
+    res = _PyObject_SIZE(Py_TYPE(mp));
     if (mp->ma_values)
         res += size * sizeof(PyObject*);
     /* If the dictionary is split, the keys portion is accounted-for
diff -r 0238eafb68da Objects/listobject.c
--- a/Objects/listobject.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Objects/listobject.c	Fri Oct 16 19:26:14 2015 +0300
@@ -2324,7 +2324,7 @@ list_sizeof(PyListObject *self)
 {
     Py_ssize_t res;
 
-    res = sizeof(PyListObject) + self->allocated * sizeof(void*);
+    res = _PyObject_SIZE(Py_TYPE(self)) + self->allocated * sizeof(void*);
     return PyLong_FromSsize_t(res);
 }
 
diff -r 0238eafb68da Objects/odictobject.c
--- a/Objects/odictobject.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Objects/odictobject.c	Fri Oct 16 19:26:14 2015 +0300
@@ -950,8 +950,6 @@ odict_sizeof(PyODictObject *od)
     if (res == -1 && PyErr_Occurred())
         return NULL;
 
-    res += sizeof(PyODictObject) - sizeof(PyDictObject);
-
     /* instance dict */
     pylong = _PyDict_SizeOf((PyDictObject *)od->od_inst_dict);
     if (pylong == NULL)
diff -r 0238eafb68da Objects/setobject.c
--- a/Objects/setobject.c	Wed Oct 14 18:25:31 2015 +0200
+++ b/Objects/setobject.c	Fri Oct 16 19:26:14 2015 +0300
@@ -2001,7 +2001,7 @@ set_sizeof(PySetObject *so)
 {
     Py_ssize_t res;
 
-    res = sizeof(PySetObject);
+    res = _PyObject_SIZE(Py_TYPE(so));
     if (so->table != so->smalltable)
         res = res + (so->mask + 1) * sizeof(setentry);
     return PyLong_FromSsize_t(res);