Index: Lib/test/test_deque.py
===================================================================
--- Lib/test/test_deque.py	(revision 88188)
+++ Lib/test/test_deque.py	(working copy)
@@ -138,6 +138,15 @@
         m.d = d
         self.assertRaises(RuntimeError, d.count, 3)
 
+        # test issue11004
+        # block advance failed after rotation aligned elements on right side of block
+        d = deque([None]*16)
+        for i in range(len(d)):
+            d.rotate(-1)
+        d.rotate(1)
+        self.assertEqual(d.count(1), 0)
+        self.assertEqual(d.count(None), 16)
+
     def test_comparisons(self):
         d = deque('xabc'); d.popleft()
         for e in [d, deque('abc'), deque('ab'), deque(), list(d)]:
Index: Modules/_collectionsmodule.c
===================================================================
--- Modules/_collectionsmodule.c	(revision 88188)
+++ Modules/_collectionsmodule.c	(working copy)
@@ -485,7 +485,8 @@
         /* Advance left block/index pair */
         leftindex++;
         if (leftindex == BLOCKLEN) {
-            assert (leftblock->rightlink != NULL);
+            if (leftblock->rightlink == NULL)
+			    break;
             leftblock = leftblock->rightlink;
             leftindex = 0;
         }
@@ -533,7 +534,8 @@
         /* Advance left block/index pair */
         leftindex++;
         if (leftindex == BLOCKLEN) {
-            assert (leftblock->rightlink != NULL);
+            if (leftblock->rightlink == NULL)
+                break;
             leftblock = leftblock->rightlink;
             leftindex = 0;
         }