diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -92,6 +92,9 @@
 // its vtable and typeinfo to libc++ rather than having all other libraries
 // using that class define their own copies.
 #  define _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
+// Give reverse_iterator<T> one data member of type T, not two.
+// Also, in C++14 and later, don't derive iterator types from std::iterator.
+#  define _LIBCPP_ABI_NO_ITERATOR_BASES
 // Enable optimized version of __do_get_(un)signed which avoids redundant copies.
 #  define _LIBCPP_ABI_OPTIMIZED_LOCALE_NUM_GET
 // Use the smallest possible integer type to represent the index of the variant.
diff --git a/libcxx/include/__memory/raw_storage_iterator.h b/libcxx/include/__memory/raw_storage_iterator.h
--- a/libcxx/include/__memory/raw_storage_iterator.h
+++ b/libcxx/include/__memory/raw_storage_iterator.h
@@ -29,15 +29,23 @@
 
 template <class _OutputIterator, class _Tp>
 class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX17 raw_storage_iterator
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
     : public iterator<output_iterator_tag,
                       _Tp,                                         // purposefully not C++03
                       ptrdiff_t,                                   // purposefully not C++03
                       _Tp*,                                        // purposefully not C++03
                       raw_storage_iterator<_OutputIterator, _Tp>&> // purposefully not C++03
+#endif
 {
 private:
     _OutputIterator __x_;
 public:
+    typedef output_iterator_tag   iterator_category;
+    typedef _Tp                   value_type;
+    typedef ptrdiff_t             difference_type;
+    typedef _Tp*                  pointer;
+    typedef raw_storage_iterator& reference;
+
     _LIBCPP_INLINE_VISIBILITY explicit raw_storage_iterator(_OutputIterator __x) : __x_(__x) {}
     _LIBCPP_INLINE_VISIBILITY raw_storage_iterator& operator*() {return *this;}
     _LIBCPP_INLINE_VISIBILITY raw_storage_iterator& operator=(const _Tp& __element)
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -366,6 +366,7 @@
     typedef traits traits_type;
     typedef basic_ostream<charT,traits> ostream_type;
 
+    constexpr ostream_iterator() noexcept = default; // C++20
     ostream_iterator(ostream_type& s);
     ostream_iterator(ostream_type& s, const charT* delimiter);
     ostream_iterator(const ostream_iterator& x);
@@ -420,6 +421,7 @@
     typedef basic_streambuf<charT,traits> streambuf_type;
     typedef basic_ostream<charT,traits>   ostream_type;
 
+    constexpr ostreambuf_iterator() noexcept = default; // C++20
     ostreambuf_iterator(ostream_type& s) noexcept;
     ostreambuf_iterator(streambuf_type* s) noexcept;
     ostreambuf_iterator& operator=(charT c);
@@ -615,14 +617,18 @@
 
 template <class _Iter>
 class _LIBCPP_TEMPLATE_VIS reverse_iterator
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
     : public iterator<typename iterator_traits<_Iter>::iterator_category,
                       typename iterator_traits<_Iter>::value_type,
                       typename iterator_traits<_Iter>::difference_type,
                       typename iterator_traits<_Iter>::pointer,
                       typename iterator_traits<_Iter>::reference>
+#endif
 {
 private:
-    /*mutable*/ _Iter __t;  // no longer used as of LWG #2360, not removed due to ABI break
+#ifndef _LIBCPP_ABI_NO_ITERATOR_BASES
+    _Iter __t;  // no longer used as of LWG #2360, not removed due to ABI break
+#endif
 
     static_assert(!__is_stashing_iterator<_Iter>::value,
       "The specified iterator type cannot be used with reverse_iterator; "
@@ -632,6 +638,7 @@
     _Iter current;
 public:
     typedef _Iter                                            iterator_type;
+    typedef typename iterator_traits<_Iter>::value_type      value_type;
     typedef typename iterator_traits<_Iter>::difference_type difference_type;
     typedef typename iterator_traits<_Iter>::reference       reference;
     typedef typename iterator_traits<_Iter>::pointer         pointer;
@@ -644,6 +651,7 @@
         bidirectional_iterator_tag>                          iterator_concept;
 #endif
 
+#ifndef _LIBCPP_ABI_NO_ITERATOR_BASES
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     reverse_iterator() : __t(), current() {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
@@ -655,6 +663,20 @@
         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
         reverse_iterator& operator=(const reverse_iterator<_Up>& __u)
             { __t = current = __u.base(); return *this; }
+#else
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+    reverse_iterator() : current() {}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+    explicit reverse_iterator(_Iter __x) : current(__x) {}
+    template <class _Up>
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+        reverse_iterator(const reverse_iterator<_Up>& __u) : current(__u.base()) {}
+    template <class _Up>
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+        reverse_iterator& operator=(const reverse_iterator<_Up>& __u)
+            { current = __u.base(); return *this; }
+#endif
+
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
     _Iter base() const {return current;}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
@@ -767,16 +789,23 @@
 
 template <class _Container>
 class _LIBCPP_TEMPLATE_VIS back_insert_iterator
-    : public iterator<output_iterator_tag,
-                      void,
-                      void,
-                      void,
-                      void>
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
+    : public iterator<output_iterator_tag, void, void, void, void>
+#endif
 {
 protected:
     _Container* container;
 public:
     typedef _Container container_type;
+    typedef output_iterator_tag iterator_category;
+    typedef void value_type;
+#if _LIBCPP_STD_VER > 17
+    typedef ptrdiff_t                       difference_type;
+#else
+    typedef void                            difference_type;
+#endif
+    typedef void pointer;
+    typedef void reference;
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 explicit back_insert_iterator(_Container& __x) : container(_VSTD::addressof(__x)) {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 back_insert_iterator& operator=(const typename _Container::value_type& __value_)
@@ -800,16 +829,23 @@
 
 template <class _Container>
 class _LIBCPP_TEMPLATE_VIS front_insert_iterator
-    : public iterator<output_iterator_tag,
-                      void,
-                      void,
-                      void,
-                      void>
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
+    : public iterator<output_iterator_tag, void, void, void, void>
+#endif
 {
 protected:
     _Container* container;
 public:
     typedef _Container container_type;
+    typedef output_iterator_tag iterator_category;
+    typedef void value_type;
+#if _LIBCPP_STD_VER > 17
+    typedef ptrdiff_t                       difference_type;
+#else
+    typedef void                            difference_type;
+#endif
+    typedef void pointer;
+    typedef void reference;
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 explicit front_insert_iterator(_Container& __x) : container(_VSTD::addressof(__x)) {}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 front_insert_iterator& operator=(const typename _Container::value_type& __value_)
@@ -833,17 +869,24 @@
 
 template <class _Container>
 class _LIBCPP_TEMPLATE_VIS insert_iterator
-    : public iterator<output_iterator_tag,
-                      void,
-                      void,
-                      void,
-                      void>
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
+    : public iterator<output_iterator_tag, void, void, void, void>
+#endif
 {
 protected:
     _Container* container;
     typename _Container::iterator iter;
 public:
     typedef _Container container_type;
+    typedef output_iterator_tag iterator_category;
+    typedef void value_type;
+#if _LIBCPP_STD_VER > 17
+    typedef ptrdiff_t                       difference_type;
+#else
+    typedef void                            difference_type;
+#endif
+    typedef void pointer;
+    typedef void reference;
 
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 insert_iterator(_Container& __x, typename _Container::iterator __i)
         : container(_VSTD::addressof(__x)), iter(__i) {}
@@ -869,12 +912,19 @@
 template <class _Tp, class _CharT = char,
           class _Traits = char_traits<_CharT>, class _Distance = ptrdiff_t>
 class _LIBCPP_TEMPLATE_VIS istream_iterator
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
     : public iterator<input_iterator_tag, _Tp, _Distance, const _Tp*, const _Tp&>
+#endif
 {
 public:
     typedef _CharT char_type;
     typedef _Traits traits_type;
     typedef basic_istream<_CharT,_Traits> istream_type;
+    typedef input_iterator_tag iterator_category;
+    typedef _Tp value_type;
+    typedef _Distance difference_type;
+    typedef const _Tp* pointer;
+    typedef const _Tp& reference;
 private:
     istream_type* __in_stream_;
     _Tp __value_;
@@ -930,13 +980,15 @@
 
 template <class _Tp, class _CharT = char, class _Traits = char_traits<_CharT> >
 class _LIBCPP_TEMPLATE_VIS ostream_iterator
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
     : public iterator<output_iterator_tag, void, void, void, void>
+#endif
 {
 public:
     typedef output_iterator_tag             iterator_category;
     typedef void                            value_type;
 #if _LIBCPP_STD_VER > 17
-    typedef std::ptrdiff_t                  difference_type;
+    typedef ptrdiff_t                       difference_type;
 #else
     typedef void                            difference_type;
 #endif
@@ -950,6 +1002,9 @@
     ostream_type* __out_stream_;
     const char_type* __delim_;
 public:
+#if _LIBCPP_STD_VER > 17
+    _LIBCPP_INLINE_VISIBILITY ostream_iterator() = default;
+#endif
     _LIBCPP_INLINE_VISIBILITY ostream_iterator(ostream_type& __s) _NOEXCEPT
         : __out_stream_(_VSTD::addressof(__s)), __delim_(nullptr) {}
     _LIBCPP_INLINE_VISIBILITY ostream_iterator(ostream_type& __s, const _CharT* __delimiter) _NOEXCEPT
@@ -969,11 +1024,18 @@
 
 template<class _CharT, class _Traits>
 class _LIBCPP_TEMPLATE_VIS istreambuf_iterator
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
     : public iterator<input_iterator_tag, _CharT,
                       typename _Traits::off_type, _CharT*,
                       _CharT>
+#endif
 {
 public:
+    typedef input_iterator_tag              iterator_category;
+    typedef _CharT                          value_type;
+    typedef typename _Traits::off_type      difference_type;
+    typedef _CharT*                         pointer;
+    typedef _CharT                          reference;
     typedef _CharT                          char_type;
     typedef _Traits                         traits_type;
     typedef typename _Traits::int_type      int_type;
@@ -1039,13 +1101,15 @@
 
 template <class _CharT, class _Traits>
 class _LIBCPP_TEMPLATE_VIS ostreambuf_iterator
+#if _LIBCPP_STD_VER <= 11 || !defined(_LIBCPP_ABI_NO_ITERATOR_BASES)
     : public iterator<output_iterator_tag, void, void, void, void>
+#endif
 {
 public:
     typedef output_iterator_tag                 iterator_category;
     typedef void                                value_type;
 #if _LIBCPP_STD_VER > 17
-    typedef std::ptrdiff_t                      difference_type;
+    typedef ptrdiff_t                           difference_type;
 #else
     typedef void                                difference_type;
 #endif
@@ -1059,6 +1123,9 @@
 private:
     streambuf_type* __sbuf_;
 public:
+#if _LIBCPP_STD_VER > 17
+    _LIBCPP_INLINE_VISIBILITY ostreambuf_iterator() = default;
+#endif
     _LIBCPP_INLINE_VISIBILITY ostreambuf_iterator(ostream_type& __s) _NOEXCEPT
         : __sbuf_(__s.rdbuf()) {}
     _LIBCPP_INLINE_VISIBILITY ostreambuf_iterator(streambuf_type* __s) _NOEXCEPT
diff --git a/libcxx/test/std/iterators/iterator.primitives/iterator.traits/cxx20_iterator_traits.compile.pass.cpp b/libcxx/test/std/iterators/iterator.primitives/iterator.traits/cxx20_iterator_traits.compile.pass.cpp
--- a/libcxx/test/std/iterators/iterator.primitives/iterator.traits/cxx20_iterator_traits.compile.pass.cpp
+++ b/libcxx/test/std/iterators/iterator.primitives/iterator.traits/cxx20_iterator_traits.compile.pass.cpp
@@ -50,12 +50,12 @@
   typename Traits::iterator_concept;
 };
 
-template <class Iter, class Category, class Diff = void>
+template <class Iter, class Category>
 constexpr bool testIOIterator() {
   using Traits = std::iterator_traits<Iter>;
   static_assert(std::same_as<typename Traits::iterator_category, Category>);
   static_assert(std::same_as<typename Traits::value_type, void>);
-  static_assert(std::same_as<typename Traits::difference_type, Diff>);
+  static_assert(std::same_as<typename Traits::difference_type, std::ptrdiff_t>);
   static_assert(std::same_as<typename Traits::reference, void>);
   static_assert(std::same_as<typename Traits::pointer, void>);
   static_assert(!has_iterator_concept_v<Traits>);
@@ -200,8 +200,8 @@
 #if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
 static_assert(testWithoutConcept<std::istreambuf_iterator<char>, char, long long, char, char*, std::input_iterator_tag>());
 static_assert(testWithoutConcept<std::move_iterator<int*>, int, std::ptrdiff_t, int&&, int*, std::random_access_iterator_tag>());
-static_assert(testIOIterator<std::ostream_iterator<int, char>, std::output_iterator_tag, std::ptrdiff_t>());
-static_assert(testIOIterator<std::ostreambuf_iterator<int, char>, std::output_iterator_tag, std::ptrdiff_t>());
+static_assert(testIOIterator<std::ostream_iterator<int, char>, std::output_iterator_tag>());
+static_assert(testIOIterator<std::ostreambuf_iterator<int, char>, std::output_iterator_tag>());
 static_assert(testConstWithoutConcept<std::cregex_iterator, std::cmatch, std::forward_iterator_tag>());
 static_assert(testConstWithoutConcept<std::cregex_token_iterator, std::csub_match, std::forward_iterator_tag>());
 #endif // !_LIBCPP_HAS_NO_LOCALIZATION
diff --git a/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/types.pass.cpp b/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/types.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/types.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/types.pass.cpp
@@ -48,7 +48,11 @@
     q.test();
     static_assert((std::is_same<typename R::container_type, C>::value), "");
     static_assert((std::is_same<typename R::value_type, void>::value), "");
+#if TEST_STD_VER <= 17
     static_assert((std::is_same<typename R::difference_type, void>::value), "");
+#else
+    static_assert((std::is_same<typename R::difference_type, std::ptrdiff_t>::value), "");
+#endif
     static_assert((std::is_same<typename R::reference, void>::value), "");
     static_assert((std::is_same<typename R::pointer, void>::value), "");
     static_assert((std::is_same<typename R::iterator_category, std::output_iterator_tag>::value), "");
diff --git a/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/types.pass.cpp b/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/types.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/types.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/types.pass.cpp
@@ -49,7 +49,11 @@
     q.test();
     static_assert((std::is_same<typename R::container_type, C>::value), "");
     static_assert((std::is_same<typename R::value_type, void>::value), "");
+#if TEST_STD_VER <= 17
     static_assert((std::is_same<typename R::difference_type, void>::value), "");
+#else
+    static_assert((std::is_same<typename R::difference_type, std::ptrdiff_t>::value), "");
+#endif
     static_assert((std::is_same<typename R::reference, void>::value), "");
     static_assert((std::is_same<typename R::pointer, void>::value), "");
     static_assert((std::is_same<typename R::iterator_category, std::output_iterator_tag>::value), "");
diff --git a/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/types.pass.cpp b/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/types.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/types.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/insert.iterators/insert.iterator/types.pass.cpp
@@ -52,7 +52,11 @@
     q.test();
     static_assert((std::is_same<typename R::container_type, C>::value), "");
     static_assert((std::is_same<typename R::value_type, void>::value), "");
+#if TEST_STD_VER <= 17
     static_assert((std::is_same<typename R::difference_type, void>::value), "");
+#else
+    static_assert((std::is_same<typename R::difference_type, std::ptrdiff_t>::value), "");
+#endif
     static_assert((std::is_same<typename R::reference, void>::value), "");
     static_assert((std::is_same<typename R::pointer, void>::value), "");
     static_assert((std::is_same<typename R::iterator_category, std::output_iterator_tag>::value), "");
diff --git a/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -19,8 +19,8 @@
 using iterator = std::ostream_iterator<int, std::ostream>;
 static_assert(!std::indirectly_readable<iterator>);
 static_assert(std::indirectly_writable<iterator, int>);
-static_assert(!std::weakly_incrementable<iterator>);
-static_assert(!std::input_or_output_iterator<iterator>);
+static_assert(std::weakly_incrementable<iterator>);
+static_assert(std::input_or_output_iterator<iterator>);
 static_assert(!std::sentinel_for<iterator, iterator>);
 static_assert(!std::sized_sentinel_for<iterator, iterator>);
 static_assert(!std::input_iterator<iterator>);
diff --git a/libcxx/test/std/iterators/stream.iterators/ostream.iterator/ostream.iterator.cons.des/default.pass.cpp b/libcxx/test/std/iterators/stream.iterators/ostream.iterator/ostream.iterator.cons.des/default.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/stream.iterators/ostream.iterator/ostream.iterator.cons.des/default.pass.cpp
@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <iterator>
+
+// class ostream_iterator
+
+// constexpr ostream_iterator() noexcept = default;
+
+#include <iterator>
+#include <string> // char_traits
+
+#include "test_macros.h"
+
+struct MyTraits : std::char_traits<char> {
+    MyTraits();  // This should not be called.
+};
+
+constexpr bool test_constexpr()
+{
+    std::ostream_iterator<int> it;
+    (void)it;
+    std::ostream_iterator<int, char, MyTraits> wit;
+    (void)wit;
+    return true;
+}
+
+int main(int, char**)
+{
+    ASSERT_NOEXCEPT(std::ostream_iterator<int>());
+    ASSERT_NOEXCEPT(std::ostream_iterator<int, char, MyTraits>());
+
+    test_constexpr();
+    static_assert(test_constexpr());
+
+    return 0;
+}
diff --git a/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -20,8 +20,8 @@
 using iterator = std::ostreambuf_iterator<char>;
 static_assert(!std::indirectly_readable<iterator>);
 static_assert(std::indirectly_writable<iterator, char>);
-static_assert(!std::weakly_incrementable<iterator>);
-static_assert(!std::input_or_output_iterator<iterator>);
+static_assert(std::weakly_incrementable<iterator>);
+static_assert(std::input_or_output_iterator<iterator>);
 static_assert(!std::sentinel_for<iterator, iterator>);
 static_assert(!std::sized_sentinel_for<iterator, iterator>);
 static_assert(!std::input_iterator<iterator>);
diff --git a/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/ostreambuf.iter.cons/default.pass.cpp b/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/ostreambuf.iter.cons/default.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/ostreambuf.iter.cons/default.pass.cpp
@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <iterator>
+
+// class ostreambuf_iterator
+
+// constexpr ostreambuf_iterator() noexcept = default;
+
+#include <iterator>
+
+#include "test_macros.h"
+
+constexpr bool test_constexpr()
+{
+    std::ostreambuf_iterator<char> it;
+    (void)it;
+    std::ostreambuf_iterator<wchar_t> wit;
+    (void)wit;
+    return true;
+}
+
+int main(int, char**)
+{
+    ASSERT_NOEXCEPT(std::ostreambuf_iterator<char>());
+    ASSERT_NOEXCEPT(std::ostreambuf_iterator<wchar_t>());
+
+    test_constexpr();
+    static_assert(test_constexpr());
+
+    return 0;
+}