Index: include/deque
===================================================================
--- include/deque
+++ include/deque
@@ -262,8 +262,19 @@
               __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1> __l,
               __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2> __r);
 
+template <class _ValueType, class _DiffType>
+struct __deque_block_size {
+  static const _DiffType value = sizeof(_ValueType) < 256 ? 4096 / sizeof(_ValueType) : 16;
+};
+
 template <class _ValueType, class _Pointer, class _Reference, class _MapPointer,
-          class _DiffType, _DiffType _BlockSize>
+          class _DiffType, _DiffType _BlockSize =
+#ifdef _LIBCPP_NEW_DEQUE_ABI
+                               0
+#else
+                               __deque_block_size<_ValueType, _DiffType>::value
+#endif
+          >
 class _LIBCPP_TYPE_VIS_ONLY __deque_iterator
 {
     typedef _MapPointer __map_iterator;
@@ -274,7 +285,7 @@
     __map_iterator __m_iter_;
     pointer        __ptr_;
 
-    static const difference_type __block_size = _BlockSize;
+    static const difference_type __block_size = __deque_block_size<_ValueType, _DiffType>::value;
 public:
     typedef _ValueType                  value_type;
     typedef random_access_iterator_tag  iterator_category;
@@ -288,7 +299,7 @@
 
     template <class _Pp, class _Rp, class _MP>
     _LIBCPP_INLINE_VISIBILITY
-    __deque_iterator(const __deque_iterator<value_type, _Pp, _Rp, _MP, difference_type, __block_size>& __it,
+    __deque_iterator(const __deque_iterator<value_type, _Pp, _Rp, _MP, difference_type, _BlockSize>& __it,
                 typename enable_if<is_convertible<_Pp, pointer>::value>::type* = 0) _NOEXCEPT
         : __m_iter_(__it.__m_iter_), __ptr_(__it.__ptr_) {}
 
@@ -533,10 +544,11 @@
 {
     typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::difference_type difference_type;
     typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::pointer pointer;
+    const difference_type __block_size = __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::__block_size;
     while (__f != __l)
     {
         pointer __rb = __r.__ptr_;
-        pointer __re = *__r.__m_iter_ + _B2;
+        pointer __re = *__r.__m_iter_ + __block_size;
         difference_type __bs = __re - __rb;
         difference_type __n = __l - __f;
         _RAIter __m = __l;
@@ -561,11 +573,12 @@
 {
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
+    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
     difference_type __n = __l - __f;
     while (__n > 0)
     {
         pointer __fb = __f.__ptr_;
-        pointer __fe = *__f.__m_iter_ + _B1;
+        pointer __fe = *__f.__m_iter_ + __block_size;
         difference_type __bs = __fe - __fb;
         if (__bs > __n)
         {
@@ -588,11 +601,12 @@
 {
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
+    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
     difference_type __n = __l - __f;
     while (__n > 0)
     {
         pointer __fb = __f.__ptr_;
-        pointer __fe = *__f.__m_iter_ + _B1;
+        pointer __fe = *__f.__m_iter_ + __block_size;
         difference_type __bs = __fe - __fb;
         if (__bs > __n)
         {
@@ -706,10 +720,11 @@
 {
     typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::difference_type difference_type;
     typedef typename __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::pointer pointer;
+    const difference_type __block_size = __deque_iterator<_V2, _P2, _R2, _M2, _D2, _B2>::__block_size;
     while (__f != __l)
     {
         pointer __rb = __r.__ptr_;
-        pointer __re = *__r.__m_iter_ + _B2;
+        pointer __re = *__r.__m_iter_ + __block_size;
         difference_type __bs = __re - __rb;
         difference_type __n = __l - __f;
         _RAIter __m = __l;
@@ -734,11 +749,12 @@
 {
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
+    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
     difference_type __n = __l - __f;
     while (__n > 0)
     {
         pointer __fb = __f.__ptr_;
-        pointer __fe = *__f.__m_iter_ + _B1;
+        pointer __fe = *__f.__m_iter_ + __block_size;
         difference_type __bs = __fe - __fb;
         if (__bs > __n)
         {
@@ -761,11 +777,12 @@
 {
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::difference_type difference_type;
     typedef typename __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::pointer pointer;
+    const difference_type __block_size = __deque_iterator<_V1, _P1, _R1, _M1, _D1, _B1>::__block_size;
     difference_type __n = __l - __f;
     while (__n > 0)
     {
         pointer __fb = __f.__ptr_;
-        pointer __fe = *__f.__m_iter_ + _B1;
+        pointer __fe = *__f.__m_iter_ + __block_size;
         difference_type __bs = __fe - __fb;
         if (__bs > __n)
         {
@@ -910,7 +927,7 @@
     typedef typename __alloc_traits::pointer         pointer;
     typedef typename __alloc_traits::const_pointer   const_pointer;
 
-    static const difference_type __block_size = sizeof(value_type) < 256 ? 4096 / sizeof(value_type) : 16;
+    static const difference_type __block_size;
 
     typedef typename __rebind_alloc_helper<__alloc_traits, pointer>::type __pointer_allocator;
     typedef allocator_traits<__pointer_allocator>        __map_traits;
@@ -920,9 +937,9 @@
     typedef __split_buffer<pointer, __pointer_allocator> __map;
 
     typedef __deque_iterator<value_type, pointer, reference, __map_pointer,
-                             difference_type, __block_size>    iterator;
+                             difference_type>    iterator;
     typedef __deque_iterator<value_type, const_pointer, const_reference, __map_const_pointer,
-                             difference_type, __block_size>    const_iterator;
+                             difference_type>    const_iterator;
 
     __map __map_;
     size_type __start_;
@@ -1014,6 +1031,11 @@
 };
 
 template <class _Tp, class _Allocator>
+const typename __deque_base<_Tp, _Allocator>::difference_type
+    __deque_base<_Tp, _Allocator>::__block_size =
+        __deque_block_size<value_type, difference_type>::value;
+
+template <class _Tp, class _Allocator>
 bool
 __deque_base<_Tp, _Allocator>::__invariants() const
 {