diff -r 60430bdcb426 Lib/test/seq_tests.py
--- a/Lib/test/seq_tests.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/seq_tests.py	Tue Mar 08 13:26:09 2016 +0200
@@ -5,6 +5,7 @@ Tests common to tuple, list and UserList
 import unittest
 import sys
 import pickle
+from test import support
 
 # Various iterables
 # This is used for checking the constructor (here and in test_deque.py)
@@ -408,3 +409,7 @@ class CommonTest(unittest.TestCase):
             lst2 = pickle.loads(pickle.dumps(lst, proto))
             self.assertEqual(lst2, lst)
             self.assertNotEqual(id(lst2), id(lst))
+
+    def test_free_after_iterating(self):
+        support.check_free_after_iterating(self, iter, self.type2test)
+        support.check_free_after_iterating(self, reversed, self.type2test)
diff -r 60430bdcb426 Lib/test/support/__init__.py
--- a/Lib/test/support/__init__.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/support/__init__.py	Tue Mar 08 13:26:09 2016 +0200
@@ -2432,3 +2432,22 @@ def run_in_subinterp(code):
                                      "memory allocations")
     import _testcapi
     return _testcapi.run_in_subinterp(code)
+
+
+def check_free_after_iterating(test, iter, cls, args=()):
+    class A(cls):
+        def __del__(self):
+            nonlocal done
+            done = True
+            try:
+                next(it)
+            except StopIteration:
+                pass
+
+    done = False
+    it = iter(A(*args))
+    # Issue 26494: Shouldn't crash
+    test.assertRaises(StopIteration, next, it)
+    # The sequence should be deallocated just after the end of iterating
+    gc_collect()
+    test.assertTrue(done)
diff -r 60430bdcb426 Lib/test/test_bytes.py
--- a/Lib/test/test_bytes.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_bytes.py	Tue Mar 08 13:26:09 2016 +0200
@@ -761,6 +761,10 @@ class BaseBytesTest:
         self.assertRaisesRegex(TypeError, r'\bendswith\b', b.endswith,
                                 x, None, None, None)
 
+    def test_free_after_iterating(self):
+        test.support.check_free_after_iterating(self, iter, self.type2test)
+        test.support.check_free_after_iterating(self, reversed, self.type2test)
+
 
 class BytesTest(BaseBytesTest, unittest.TestCase):
     type2test = bytes
diff -r 60430bdcb426 Lib/test/test_deque.py
--- a/Lib/test/test_deque.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_deque.py	Tue Mar 08 13:26:09 2016 +0200
@@ -918,6 +918,9 @@ class TestSequence(seq_tests.CommonTest)
         # For now, bypass tests that require slicing
         pass
 
+    # Exhausted deque iterator doesn't free a deque
+    test_free_after_iterating = None
+
 #==============================================================================
 
 libreftest = """
diff -r 60430bdcb426 Lib/test/test_dict.py
--- a/Lib/test/test_dict.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_dict.py	Tue Mar 08 13:26:09 2016 +0200
@@ -954,6 +954,12 @@ class DictTest(unittest.TestCase):
         d = {X(): 0, 1: 1}
         self.assertRaises(RuntimeError, d.update, other)
 
+    def test_free_after_iterating(self):
+        support.check_free_after_iterating(self, iter, dict)
+        support.check_free_after_iterating(self, lambda d: iter(d.keys()), dict)
+        support.check_free_after_iterating(self, lambda d: iter(d.values()), dict)
+        support.check_free_after_iterating(self, lambda d: iter(d.items()), dict)
+
 from test import mapping_tests
 
 class GeneralMappingTests(mapping_tests.BasicTestMappingProtocol):
diff -r 60430bdcb426 Lib/test/test_iter.py
--- a/Lib/test/test_iter.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_iter.py	Tue Mar 08 13:26:09 2016 +0200
@@ -3,6 +3,7 @@
 import sys
 import unittest
 from test.support import run_unittest, TESTFN, unlink, cpython_only
+from test.support import check_free_after_iterating
 import pickle
 import collections.abc
 
@@ -980,6 +981,9 @@ class TestCase(unittest.TestCase):
         self.assertEqual(next(it), 0)
         self.assertEqual(next(it), 1)
 
+    def test_free_after_iterating(self):
+        check_free_after_iterating(self, iter, SequenceClass, (0,))
+
 
 def test_main():
     run_unittest(TestCase)
diff -r 60430bdcb426 Lib/test/test_ordered_dict.py
--- a/Lib/test/test_ordered_dict.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_ordered_dict.py	Tue Mar 08 13:26:09 2016 +0200
@@ -608,6 +608,12 @@ class OrderedDictTests:
         gc.collect()
         self.assertIsNone(r())
 
+    def test_free_after_iterating(self):
+        support.check_free_after_iterating(self, iter, self.OrderedDict)
+        support.check_free_after_iterating(self, lambda d: iter(d.keys()), self.OrderedDict)
+        support.check_free_after_iterating(self, lambda d: iter(d.values()), self.OrderedDict)
+        support.check_free_after_iterating(self, lambda d: iter(d.items()), self.OrderedDict)
+
 
 class PurePythonOrderedDictTests(OrderedDictTests, unittest.TestCase):
 
diff -r 60430bdcb426 Lib/test/test_set.py
--- a/Lib/test/test_set.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_set.py	Tue Mar 08 13:26:09 2016 +0200
@@ -364,6 +364,9 @@ class TestJointOps:
         gc.collect()
         self.assertTrue(ref() is None, "Cycle was not collected")
 
+    def test_free_after_iterating(self):
+        support.check_free_after_iterating(self, iter, self.thetype)
+
 class TestSet(TestJointOps, unittest.TestCase):
     thetype = set
     basetype = set
diff -r 60430bdcb426 Lib/test/test_unicode.py
--- a/Lib/test/test_unicode.py	Tue Mar 08 01:11:14 2016 -0500
+++ b/Lib/test/test_unicode.py	Tue Mar 08 13:26:09 2016 +0200
@@ -2729,6 +2729,10 @@ class UnicodeTest(string_tests.CommonTes
                 # Check that the second call returns the same result
                 self.assertEqual(getargs_s_hash(s), chr(k).encode() * (i + 1))
 
+    def test_free_after_iterating(self):
+        support.check_free_after_iterating(self, iter, str)
+        support.check_free_after_iterating(self, reversed, str)
+
 
 class StringModuleTest(unittest.TestCase):
     def test_formatter_parser(self):
diff -r 60430bdcb426 Modules/posixmodule.c
--- a/Modules/posixmodule.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Modules/posixmodule.c	Tue Mar 08 13:26:09 2016 +0200
@@ -11946,13 +11946,15 @@ ScandirIterator_is_closed(ScandirIterato
 static void
 ScandirIterator_closedir(ScandirIterator *iterator)
 {
-    if (iterator->handle == INVALID_HANDLE_VALUE)
+    HANDLE handle = iterator->handle;
+
+    if (handle == INVALID_HANDLE_VALUE)
         return;
 
+    iterator->handle = INVALID_HANDLE_VALUE;
     Py_BEGIN_ALLOW_THREADS
-    FindClose(iterator->handle);
+    FindClose(handle);
     Py_END_ALLOW_THREADS
-    iterator->handle = INVALID_HANDLE_VALUE;
 }
 
 static PyObject *
@@ -12008,13 +12010,15 @@ ScandirIterator_is_closed(ScandirIterato
 static void
 ScandirIterator_closedir(ScandirIterator *iterator)
 {
-    if (!iterator->dirp)
+    DIR *dirp = iterator->dirp;
+
+    if (!dirp)
         return;
 
+    iterator->dirp = NULL;
     Py_BEGIN_ALLOW_THREADS
-    closedir(iterator->dirp);
+    closedir(dirp);
     Py_END_ALLOW_THREADS
-    iterator->dirp = NULL;
     return;
 }
 
diff -r 60430bdcb426 Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/bytearrayobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -3116,8 +3116,8 @@ bytearrayiter_next(bytesiterobject *it)
         return item;
     }
 
+    it->it_seq = NULL;
     Py_DECREF(seq);
-    it->it_seq = NULL;
     return NULL;
 }
 
diff -r 60430bdcb426 Objects/bytesobject.c
--- a/Objects/bytesobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/bytesobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -3796,8 +3796,8 @@ striter_next(striterobject *it)
         return item;
     }
 
+    it->it_seq = NULL;
     Py_DECREF(seq);
-    it->it_seq = NULL;
     return NULL;
 }
 
diff -r 60430bdcb426 Objects/dictobject.c
--- a/Objects/dictobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/dictobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -2988,8 +2988,8 @@ static PyObject *dictiter_iternextkey(di
     return key;
 
 fail:
+    di->di_dict = NULL;
     Py_DECREF(d);
-    di->di_dict = NULL;
     return NULL;
 }
 
@@ -3069,8 +3069,8 @@ static PyObject *dictiter_iternextvalue(
     return value;
 
 fail:
+    di->di_dict = NULL;
     Py_DECREF(d);
-    di->di_dict = NULL;
     return NULL;
 }
 
@@ -3164,8 +3164,8 @@ static PyObject *dictiter_iternextitem(d
     return result;
 
 fail:
+    di->di_dict = NULL;
     Py_DECREF(d);
-    di->di_dict = NULL;
     return NULL;
 }
 
diff -r 60430bdcb426 Objects/listobject.c
--- a/Objects/listobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/listobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -2776,8 +2776,8 @@ listiter_next(listiterobject *it)
         return item;
     }
 
+    it->it_seq = NULL;
     Py_DECREF(seq);
-    it->it_seq = NULL;
     return NULL;
 }
 
@@ -2906,9 +2906,17 @@ static PyObject *
 listreviter_next(listreviterobject *it)
 {
     PyObject *item;
-    Py_ssize_t index = it->it_index;
-    PyListObject *seq = it->it_seq;
+    Py_ssize_t index;
+    PyListObject *seq;
 
+    assert(it != NULL);
+    seq = it->it_seq;
+    if (seq == NULL) {
+        return NULL;
+    }
+    assert(PyList_Check(seq));
+
+    index = it->it_index;
     if (index>=0 && index < PyList_GET_SIZE(seq)) {
         item = PyList_GET_ITEM(seq, index);
         it->it_index--;
@@ -2916,10 +2924,8 @@ listreviter_next(listreviterobject *it)
         return item;
     }
     it->it_index = -1;
-    if (seq != NULL) {
-        it->it_seq = NULL;
-        Py_DECREF(seq);
-    }
+    it->it_seq = NULL;
+    Py_DECREF(seq);
     return NULL;
 }
 
diff -r 60430bdcb426 Objects/setobject.c
--- a/Objects/setobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/setobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -916,8 +916,8 @@ static PyObject *setiter_iternext(setite
     return key;
 
 fail:
+    si->si_set = NULL;
     Py_DECREF(so);
-    si->si_set = NULL;
     return NULL;
 }
 
diff -r 60430bdcb426 Objects/tupleobject.c
--- a/Objects/tupleobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/tupleobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -961,8 +961,8 @@ tupleiter_next(tupleiterobject *it)
         return item;
     }
 
+    it->it_seq = NULL;
     Py_DECREF(seq);
-    it->it_seq = NULL;
     return NULL;
 }
 
diff -r 60430bdcb426 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Tue Mar 08 01:11:14 2016 -0500
+++ b/Objects/unicodeobject.c	Tue Mar 08 13:26:09 2016 +0200
@@ -15401,8 +15401,8 @@ unicodeiter_next(unicodeiterobject *it)
         return item;
     }
 
+    it->it_seq = NULL;
     Py_DECREF(seq);
-    it->it_seq = NULL;
     return NULL;
 }