diff -r e33b4c18af59 Lib/test/test_deque.py
--- a/Lib/test/test_deque.py	Wed Sep 16 12:18:55 2015 -0400
+++ b/Lib/test/test_deque.py	Thu Sep 17 17:08:05 2015 +0300
@@ -474,13 +474,14 @@ class TestBasic(unittest.TestCase):
         self.assertRaises(IndexError, d.popleft)
 
     def test_clear(self):
-        d = deque(range(100))
-        self.assertEqual(len(d), 100)
-        d.clear()
-        self.assertEqual(len(d), 0)
-        self.assertEqual(list(d), [])
-        d.clear()               # clear an emtpy deque
-        self.assertEqual(list(d), [])
+        for n in range(1, 101):
+            d = deque(range(n))
+            self.assertEqual(len(d), n)
+            d.clear()
+            self.assertEqual(len(d), 0)
+            self.assertEqual(list(d), [])
+            d.clear()               # clear an emtpy deque
+            self.assertEqual(list(d), [])
 
     def test_remove(self):
         d = deque('abcdefghcij')
diff -r e33b4c18af59 Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c	Wed Sep 16 12:18:55 2015 -0400
+++ b/Modules/_collectionsmodule.c	Thu Sep 17 17:08:05 2015 +0300
@@ -1045,16 +1045,61 @@ PyDoc_STRVAR(remove_doc,
 static void
 deque_clear(dequeobject *deque)
 {
+    block *b;
+    block *prevblock;
+    block *leftblock = deque->leftblock;
+    Py_ssize_t leftindex = deque->leftindex;
+#ifndef NDEBUG
+    Py_ssize_t rightindex = deque->rightindex;
+#endif
+    Py_ssize_t n = Py_SIZE(deque);
     PyObject *item;
+    block tmp; /* a copy of right block */
 
-    while (Py_SIZE(deque)) {
-        item = deque_pop(deque, NULL);
-        assert (item != NULL);
+    /* During the process of clearing a deque, decrefs can cause the
+       deque to mutate.  To avoid fatal confusion, we have to make the
+       deque empty before clearing the blocks and never refer to
+       anything via deque->ref while clearing.  (This is the same
+       technique used in the clearing functions for lists, sets, and
+       dicts.)
+    */
+
+    b = deque->rightblock;
+    memcpy(tmp.data, b->data, sizeof(PyObject *) * BLOCKLEN);
+    MARK_END(tmp.rightlink);
+    if (b == leftblock)
+        leftblock = &tmp;
+    else {
+        CHECK_NOT_END(b->leftlink);
+        assert(b->leftlink->rightlink == b);
+        b->leftlink->rightlink = &tmp;
+    }
+#ifndef NDEBUG
+    memset(b->data, 0, sizeof(PyObject *) * BLOCKLEN);
+#endif
+    MARK_END(b->leftlink);
+    MARK_END(b->rightlink);
+    Py_SIZE(deque) = 0;
+    deque->leftblock = b;
+    deque->rightblock = b;
+    deque->leftindex = CENTER + 1;
+    deque->rightindex = CENTER;
+    deque->state++;
+
+    /* Now use the old size, leftblock, and leftindex to decref the pointers */
+    while (n--) {
+        item = leftblock->data[leftindex];
         Py_DECREF(item);
+        leftindex++;
+        if (leftindex == BLOCKLEN && n) {
+            prevblock = leftblock;
+            leftblock = leftblock->rightlink;
+            leftindex = 0;
+            freeblock(prevblock);
+        }
     }
-    assert(deque->leftblock == deque->rightblock);
-    assert(deque->leftindex - 1 == deque->rightindex);
-    assert(Py_SIZE(deque) == 0);
+    assert(leftblock == &tmp);
+    assert(leftindex == rightindex + 1);
 }
 
 static int