Index: include/iterator
===================================================================
--- include/iterator	(revision 187794)
+++ include/iterator	(working copy)
@@ -1093,6 +1093,9 @@
     iterator_type __i;
 public:
     _LIBCPP_INLINE_VISIBILITY __wrap_iter() _NOEXCEPT
+#if _LIBCPP_STD_VER > 11
+				: __i{}
+#endif
     {
 #if _LIBCPP_DEBUG_LEVEL >= 2
         __get_db()->__insert_i(this);
Index: test/strings/basic.string/string.iterators/iterators.pass.cpp
===================================================================
--- test/strings/basic.string/string.iterators/iterators.pass.cpp	(revision 0)
+++ test/strings/basic.string/string.iterators/iterators.pass.cpp	(revision 0)
@@ -0,0 +1,105 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <string>
+
+// iterator       begin();
+// iterator       end();
+// const_iterator begin()  const;
+// const_iterator end()    const;
+// const_iterator cbegin() const;
+// const_iterator cend()   const;
+
+#include <string>
+#include <cassert>
+
+int main()
+{
+#if _LIBCPP_STD_VER > 11
+    { // N3664 testing
+        typedef std::string C;
+        C::iterator ii1{}, ii2{};
+        C::iterator ii3;
+        C::iterator ii4 = ii1;
+        C::const_iterator cii{};
+        assert ( ii1 == ii2 );
+        assert ( ii1 == ii3 );
+        assert ( ii1 == ii4 );
+        
+//         C c;
+//         assert ( ii1 != c.cbegin());
+//         assert ( cii != c.begin());
+//         assert ( !(ii2 == c.end()));
+        
+        assert ( ii1 == cii );
+        assert ( !(ii1 != ii2 ));
+        assert ( !(ii1 != cii ));
+    }
+
+    { // N3664 testing
+        typedef std::wstring C;
+        C::iterator ii1{}, ii2{};
+        C::iterator ii3;
+        C::iterator ii4 = ii1;
+        C::const_iterator cii{};
+        assert ( ii1 == ii2 );
+        assert ( ii1 == ii3 );
+        assert ( ii1 == ii4 );
+        
+//         C c;
+//         assert ( ii1 != c.cbegin());
+//         assert ( cii != c.begin());
+//         assert ( !(ii2 == c.end()));
+        
+        assert ( ii1 == cii );
+        assert ( !(ii1 != ii2 ));
+        assert ( !(ii1 != cii ));
+    }
+
+    { // N3664 testing
+        typedef std::u16string C;
+        C::iterator ii1{}, ii2{};
+        C::iterator ii3;
+        C::iterator ii4 = ii1;
+        C::const_iterator cii{};
+        assert ( ii1 == ii2 );
+        assert ( ii1 == ii3 );
+        assert ( ii1 == ii4 );
+        
+//         C c;
+//         assert ( ii1 != c.cbegin());
+//         assert ( cii != c.begin());
+//         assert ( !(ii2 == c.end()));
+        
+        assert ( ii1 == cii );
+        assert ( !(ii1 != ii2 ));
+        assert ( !(ii1 != cii ));
+    }
+
+    { // N3664 testing
+        typedef std::u32string C;
+        C::iterator ii1{}, ii2{};
+        C::iterator ii3;
+        C::iterator ii4 = ii1;
+        C::const_iterator cii{};
+        assert ( ii1 == ii2 );
+        assert ( ii1 == ii3 );
+        assert ( ii1 == ii4 );
+        
+//         C c;
+//         assert ( ii1 != c.cbegin());
+//         assert ( cii != c.begin());
+//         assert ( !(ii2 == c.end()));
+        
+        assert ( ii1 == cii );
+        assert ( !(ii1 != ii2 ));
+        assert ( !(ii1 != cii ));
+    }
+#endif
+}
Index: test/containers/sequences/vector/iterators.pass.cpp
===================================================================
--- test/containers/sequences/vector/iterators.pass.cpp	(revision 187794)
+++ test/containers/sequences/vector/iterators.pass.cpp	(working copy)
@@ -135,4 +135,25 @@
         assert(j->first == 3);
     }
 #endif
+#if _LIBCPP_STD_VER > 11
+    { // N3664 testing
+        typedef std::vector<int> C;
+        C::iterator ii1{}, ii2{};
+        C::iterator ii3;
+        C::iterator ii4 = ii1;
+        C::const_iterator cii{};
+        assert ( ii1 == ii2 );
+        assert ( ii1 == ii3 );
+        assert ( ii1 == ii4 );
+        
+//         C c;
+//         assert ( ii1 != c.cbegin());
+//         assert ( cii != c.begin());
+//         assert ( !(ii2 == c.end()));
+        
+        assert ( ii1 == cii );
+        assert ( !(ii1 != ii2 ));
+        assert ( !(ii1 != cii ));
+    }
+#endif
 }