diff --git a/libcxx/include/__debug b/libcxx/include/__debug
--- a/libcxx/include/__debug
+++ b/libcxx/include/__debug
@@ -116,7 +116,7 @@
 inline bool
 _C_node<_Cont>::__dereferenceable(const void* __i) const
 {
-    typedef typename _Cont::const_iterator iterator;
+    typedef typename _Cont::__debug_iterator iterator;
     const iterator* __j = static_cast<const iterator*>(__i);
     _Cont* _Cp = static_cast<_Cont*>(__c_);
     return _Cp->__dereferenceable(__j);
@@ -126,7 +126,7 @@
 inline bool
 _C_node<_Cont>::__decrementable(const void* __i) const
 {
-    typedef typename _Cont::const_iterator iterator;
+    typedef typename _Cont::__debug_iterator iterator;
     const iterator* __j = static_cast<const iterator*>(__i);
     _Cont* _Cp = static_cast<_Cont*>(__c_);
     return _Cp->__decrementable(__j);
@@ -136,7 +136,7 @@
 inline bool
 _C_node<_Cont>::__addable(const void* __i, ptrdiff_t __n) const
 {
-    typedef typename _Cont::const_iterator iterator;
+    typedef typename _Cont::__debug_iterator iterator;
     const iterator* __j = static_cast<const iterator*>(__i);
     _Cont* _Cp = static_cast<_Cont*>(__c_);
     return _Cp->__addable(__j, __n);
@@ -146,7 +146,7 @@
 inline bool
 _C_node<_Cont>::__subscriptable(const void* __i, ptrdiff_t __n) const
 {
-    typedef typename _Cont::const_iterator iterator;
+    typedef typename _Cont::__debug_iterator iterator;
     const iterator* __j = static_cast<const iterator*>(__i);
     _Cont* _Cp = static_cast<_Cont*>(__c_);
     return _Cp->__subscriptable(__j, __n);
diff --git a/libcxx/include/__hash_table b/libcxx/include/__hash_table
--- a/libcxx/include/__hash_table
+++ b/libcxx/include/__hash_table
@@ -1283,10 +1283,11 @@
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 
-    bool __dereferenceable(const const_iterator* __i) const;
-    bool __decrementable(const const_iterator* __i) const;
-    bool __addable(const const_iterator* __i, ptrdiff_t __n) const;
-    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const;
+    using __debug_iterator = const_iterator;
+    bool __dereferenceable(const __debug_iterator* __i) const;
+    bool __decrementable(const __debug_iterator* __i) const;
+    bool __addable(const __debug_iterator* __i, ptrdiff_t __n) const;
+    bool __subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const;
 
 #endif // _LIBCPP_ENABLE_DEBUG_MODE
 
@@ -2667,28 +2668,28 @@
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 bool
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__dereferenceable(const const_iterator* __i) const
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__dereferenceable(const __debug_iterator* __i) const
 {
     return __i->__node_ != nullptr;
 }
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 bool
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__decrementable(const const_iterator*) const
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__decrementable(const __debug_iterator*) const
 {
     return false;
 }
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 bool
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__addable(const const_iterator*, ptrdiff_t) const
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__addable(const __debug_iterator*, ptrdiff_t) const
 {
     return false;
 }
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 bool
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__subscriptable(const const_iterator*, ptrdiff_t) const
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__subscriptable(const __debug_iterator*, ptrdiff_t) const
 {
     return false;
 }
diff --git a/libcxx/include/list b/libcxx/include/list
--- a/libcxx/include/list
+++ b/libcxx/include/list
@@ -1077,10 +1077,11 @@
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 
-    bool __dereferenceable(const const_iterator* __i) const;
-    bool __decrementable(const const_iterator* __i) const;
-    bool __addable(const const_iterator* __i, ptrdiff_t __n) const;
-    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const;
+    using __debug_iterator = const_iterator;
+    bool __dereferenceable(const __debug_iterator* __i) const;
+    bool __decrementable(const __debug_iterator* __i) const;
+    bool __addable(const __debug_iterator* __i, ptrdiff_t __n) const;
+    bool __subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const;
 
 #endif // _LIBCPP_ENABLE_DEBUG_MODE
 
@@ -2229,28 +2230,28 @@
 
 template <class _Tp, class _Alloc>
 bool
-list<_Tp, _Alloc>::__dereferenceable(const const_iterator* __i) const
+list<_Tp, _Alloc>::__dereferenceable(const __debug_iterator* __i) const
 {
     return __i->__ptr_ != this->__end_as_link();
 }
 
 template <class _Tp, class _Alloc>
 bool
-list<_Tp, _Alloc>::__decrementable(const const_iterator* __i) const
+list<_Tp, _Alloc>::__decrementable(const __debug_iterator* __i) const
 {
     return !empty() &&  __i->__ptr_ != base::__end_.__next_;
 }
 
 template <class _Tp, class _Alloc>
 bool
-list<_Tp, _Alloc>::__addable(const const_iterator*, ptrdiff_t) const
+list<_Tp, _Alloc>::__addable(const __debug_iterator*, ptrdiff_t) const
 {
     return false;
 }
 
 template <class _Tp, class _Alloc>
 bool
-list<_Tp, _Alloc>::__subscriptable(const const_iterator*, ptrdiff_t) const
+list<_Tp, _Alloc>::__subscriptable(const __debug_iterator*, ptrdiff_t) const
 {
     return false;
 }
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1452,10 +1452,11 @@
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 
-    bool __dereferenceable(const const_iterator* __i) const;
-    bool __decrementable(const const_iterator* __i) const;
-    bool __addable(const const_iterator* __i, ptrdiff_t __n) const;
-    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const;
+    using __debug_iterator = const_iterator;
+    bool __dereferenceable(const __debug_iterator* __i) const;
+    bool __decrementable(const __debug_iterator* __i) const;
+    bool __addable(const __debug_iterator* __i, ptrdiff_t __n) const;
+    bool __subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const;
 
 #endif // _LIBCPP_ENABLE_DEBUG_MODE
 
@@ -4599,7 +4600,7 @@
 
 template<class _CharT, class _Traits, class _Allocator>
 bool
-basic_string<_CharT, _Traits, _Allocator>::__dereferenceable(const const_iterator* __i) const
+basic_string<_CharT, _Traits, _Allocator>::__dereferenceable(const __debug_iterator* __i) const
 {
     return data() <= std::__to_address(__i->base()) &&
            std::__to_address(__i->base()) < data() + size();
@@ -4607,7 +4608,7 @@
 
 template<class _CharT, class _Traits, class _Allocator>
 bool
-basic_string<_CharT, _Traits, _Allocator>::__decrementable(const const_iterator* __i) const
+basic_string<_CharT, _Traits, _Allocator>::__decrementable(const __debug_iterator* __i) const
 {
     return data() < std::__to_address(__i->base()) &&
            std::__to_address(__i->base()) <= data() + size();
@@ -4615,7 +4616,7 @@
 
 template<class _CharT, class _Traits, class _Allocator>
 bool
-basic_string<_CharT, _Traits, _Allocator>::__addable(const const_iterator* __i, ptrdiff_t __n) const
+basic_string<_CharT, _Traits, _Allocator>::__addable(const __debug_iterator* __i, ptrdiff_t __n) const
 {
     const value_type* __p = std::__to_address(__i->base()) + __n;
     return data() <= __p && __p <= data() + size();
@@ -4623,7 +4624,7 @@
 
 template<class _CharT, class _Traits, class _Allocator>
 bool
-basic_string<_CharT, _Traits, _Allocator>::__subscriptable(const const_iterator* __i, ptrdiff_t __n) const
+basic_string<_CharT, _Traits, _Allocator>::__subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const
 {
     const value_type* __p = std::__to_address(__i->base()) + __n;
     return data() <= __p && __p < data() + size();
diff --git a/libcxx/include/unordered_map b/libcxx/include/unordered_map
--- a/libcxx/include/unordered_map
+++ b/libcxx/include/unordered_map
@@ -1514,13 +1514,14 @@
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 
-    bool __dereferenceable(const const_iterator* __i) const
+    using __debug_iterator = const_iterator;
+    bool __dereferenceable(const __debug_iterator* __i) const
         {return __table_.__dereferenceable(_VSTD::addressof(__i->__i_));}
-    bool __decrementable(const const_iterator* __i) const
+    bool __decrementable(const __debug_iterator* __i) const
         {return __table_.__decrementable(_VSTD::addressof(__i->__i_));}
-    bool __addable(const const_iterator* __i, ptrdiff_t __n) const
+    bool __addable(const __debug_iterator* __i, ptrdiff_t __n) const
         {return __table_.__addable(_VSTD::addressof(__i->__i_), __n);}
-    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const
+    bool __subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const
         {return __table_.__addable(_VSTD::addressof(__i->__i_), __n);}
 
 #endif // _LIBCPP_ENABLE_DEBUG_MODE
diff --git a/libcxx/include/unordered_set b/libcxx/include/unordered_set
--- a/libcxx/include/unordered_set
+++ b/libcxx/include/unordered_set
@@ -845,13 +845,14 @@
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 
-    bool __dereferenceable(const const_iterator* __i) const
+    using __debug_iterator = const_iterator;
+    bool __dereferenceable(const __debug_iterator* __i) const
         {return __table_.__dereferenceable(__i);}
-    bool __decrementable(const const_iterator* __i) const
+    bool __decrementable(const __debug_iterator* __i) const
         {return __table_.__decrementable(__i);}
-    bool __addable(const const_iterator* __i, ptrdiff_t __n) const
+    bool __addable(const __debug_iterator* __i, ptrdiff_t __n) const
         {return __table_.__addable(__i, __n);}
-    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const
+    bool __subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const
         {return __table_.__addable(__i, __n);}
 
 #endif // _LIBCPP_ENABLE_DEBUG_MODE
diff --git a/libcxx/include/vector b/libcxx/include/vector
--- a/libcxx/include/vector
+++ b/libcxx/include/vector
@@ -636,10 +636,11 @@
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
 
-    bool __dereferenceable(const const_iterator* __i) const;
-    bool __decrementable(const const_iterator* __i) const;
-    bool __addable(const const_iterator* __i, ptrdiff_t __n) const;
-    bool __subscriptable(const const_iterator* __i, ptrdiff_t __n) const;
+    using __debug_iterator = const_iterator;
+    bool __dereferenceable(const __debug_iterator* __i) const;
+    bool __decrementable(const __debug_iterator* __i) const;
+    bool __addable(const __debug_iterator* __i, ptrdiff_t __n) const;
+    bool __subscriptable(const __debug_iterator* __i, ptrdiff_t __n) const;
 
 #endif // _LIBCPP_ENABLE_DEBUG_MODE