diff --git a/libcxx/include/__bit_reference b/libcxx/include/__bit_reference
--- a/libcxx/include/__bit_reference
+++ b/libcxx/include/__bit_reference
@@ -84,7 +84,7 @@
         {return __bit_iterator<_Cp, false>(__seg_, static_cast<unsigned>(__libcpp_ctz(__mask_)));}
 private:
     _LIBCPP_INLINE_VISIBILITY
-    __bit_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
+    explicit __bit_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
         : __seg_(__s), __mask_(__m) {}
 };
 
@@ -160,7 +160,7 @@
 private:
     _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR
-    __bit_const_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
+    explicit __bit_const_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
         : __seg_(__s), __mask_(__m) {}
 
     __bit_const_reference& operator=(const __bit_const_reference&) = delete;
@@ -1246,7 +1246,7 @@
 
 private:
     _LIBCPP_INLINE_VISIBILITY
-    __bit_iterator(__storage_pointer __s, unsigned __ctz) _NOEXCEPT
+    explicit __bit_iterator(__storage_pointer __s, unsigned __ctz) _NOEXCEPT
         : __seg_(__s), __ctz_(__ctz) {}
 
     friend typename _Cp::__self;
diff --git a/libcxx/include/__debug b/libcxx/include/__debug
--- a/libcxx/include/__debug
+++ b/libcxx/include/__debug
@@ -118,7 +118,7 @@
 public:
 #endif
     _LIBCPP_INLINE_VISIBILITY
-    __c_node(void* __c, __c_node* __next)
+    explicit __c_node(void* __c, __c_node* __next)
         : __c_(__c), __next_(__next), beg_(nullptr), end_(nullptr), cap_(nullptr) {}
     virtual ~__c_node();
 
@@ -135,7 +135,7 @@
 struct _C_node
     : public __c_node
 {
-    _C_node(void* __c, __c_node* __n)
+    explicit _C_node(void* __c, __c_node* __n)
         : __c_node(__c, __n) {}
 
     virtual bool __dereferenceable(const void*) const;
@@ -193,7 +193,7 @@
     __i_node** __iend_;
     size_t   __isz_;
 
-    __libcpp_db();
+    explicit __libcpp_db();
 public:
 #ifndef _LIBCPP_CXX03_LANG
     __libcpp_db(const __libcpp_db&) = delete;
diff --git a/libcxx/include/__iterator/common_iterator.h b/libcxx/include/__iterator/common_iterator.h
--- a/libcxx/include/__iterator/common_iterator.h
+++ b/libcxx/include/__iterator/common_iterator.h
@@ -42,7 +42,7 @@
 
     iter_value_t<_Iter> __value;
     // We can move __x because the only caller verifies that __x is not a reference.
-    constexpr __proxy(iter_reference_t<_Iter>&& __x)
+    constexpr explicit __proxy(iter_reference_t<_Iter>&& __x)
       : __value(_VSTD::move(__x)) {}
 
   public:
@@ -55,7 +55,7 @@
     friend common_iterator;
 
     iter_value_t<_Iter> __value;
-    constexpr __postfix_proxy(iter_reference_t<_Iter>&& __x)
+    constexpr explicit __postfix_proxy(iter_reference_t<_Iter>&& __x)
       : __value(_VSTD::forward<iter_reference_t<_Iter>>(__x)) {}
 
   public:
diff --git a/libcxx/include/__iterator/istreambuf_iterator.h b/libcxx/include/__iterator/istreambuf_iterator.h
--- a/libcxx/include/__iterator/istreambuf_iterator.h
+++ b/libcxx/include/__iterator/istreambuf_iterator.h
@@ -49,7 +49,8 @@
     {
         char_type __keep_;
         streambuf_type* __sbuf_;
-        _LIBCPP_INLINE_VISIBILITY __proxy(char_type __c, streambuf_type* __s)
+        _LIBCPP_INLINE_VISIBILITY
+        explicit __proxy(char_type __c, streambuf_type* __s)
             : __keep_(__c), __sbuf_(__s) {}
         friend class istreambuf_iterator;
     public:
diff --git a/libcxx/include/__memory/compressed_pair.h b/libcxx/include/__memory/compressed_pair.h
--- a/libcxx/include/__memory/compressed_pair.h
+++ b/libcxx/include/__memory/compressed_pair.h
@@ -32,18 +32,19 @@
   using reference = _Tp&;
   using const_reference = const _Tp&;
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __compressed_pair_elem(__default_init_tag) {}
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __compressed_pair_elem(__value_init_tag) : __value_() {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__default_init_tag) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__value_init_tag) : __value_() {}
 
   template <class _Up, class = __enable_if_t<!is_same<__compressed_pair_elem, typename decay<_Up>::type>::value> >
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit
-  __compressed_pair_elem(_Up&& __u) : __value_(std::forward<_Up>(__u)) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
+  explicit __compressed_pair_elem(_Up&& __u) : __value_(std::forward<_Up>(__u)) {}
 
 #ifndef _LIBCPP_CXX03_LANG
-  template <class... _Args, size_t... _Indices>
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14
-  __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args, __tuple_indices<_Indices...>)
-      : __value_(std::forward<_Args>(std::get<_Indices>(__args))...) {}
+  template <class... _Args, size_t... _Indexes>
+  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+  explicit __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args,
+                         __tuple_indices<_Indexes...>)
+      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
 #endif
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11 reference __get() _NOEXCEPT { return __value_; }
@@ -60,9 +61,9 @@
   using const_reference = const _Tp&;
   using __value_type = _Tp;
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __compressed_pair_elem() = default;
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __compressed_pair_elem(__default_init_tag) {}
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __compressed_pair_elem(__value_init_tag) : __value_type() {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem() = default;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__default_init_tag) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__value_init_tag) : __value_type() {}
 
   template <class _Up, class = __enable_if_t<!is_same<__compressed_pair_elem, typename decay<_Up>::type>::value> >
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
@@ -101,17 +102,17 @@
     >
   >
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
-  __compressed_pair() : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
+  explicit __compressed_pair() : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
 
   template <class _U1, class _U2>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
-  __compressed_pair(_U1&& __t1, _U2&& __t2) : _Base1(std::forward<_U1>(__t1)), _Base2(std::forward<_U2>(__t2)) {}
+  explicit __compressed_pair(_U1&& __t1, _U2&& __t2) : _Base1(std::forward<_U1>(__t1)), _Base2(std::forward<_U2>(__t2)) {}
 
 #ifndef _LIBCPP_CXX03_LANG
   template <class... _Args1, class... _Args2>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14
-  __compressed_pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
-                    tuple<_Args2...> __second_args)
+  explicit __compressed_pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
+                             tuple<_Args2...> __second_args)
       : _Base1(__pc, std::move(__first_args), typename __make_tuple_indices<sizeof...(_Args1)>::type()),
         _Base2(__pc, std::move(__second_args), typename __make_tuple_indices<sizeof...(_Args2)>::type()) {}
 #endif
diff --git a/libcxx/include/iomanip b/libcxx/include/iomanip
--- a/libcxx/include/iomanip
+++ b/libcxx/include/iomanip
@@ -573,7 +573,7 @@
          basic_ostream<_CharT, _Traits>& __os,
          const __quoted_output_proxy<_CharT, _Iter, _Traits> & __proxy)
 {
-    return __quoted_output (__os, __proxy.__first, __proxy.__last, __proxy.__delim, __proxy.__escape);
+    return __quoted_output(__os, __proxy.__first, __proxy.__last, __proxy.__delim, __proxy.__escape);
 }
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -583,8 +583,8 @@
     _CharT  __delim;
     _CharT  __escape;
 
-    __quoted_proxy(basic_string<_CharT, _Traits, _Allocator> &__s, _CharT __d, _CharT __e)
-    : __string(__s), __delim(__d), __escape(__e) {}
+    explicit __quoted_proxy(basic_string<_CharT, _Traits, _Allocator> &__s, _CharT __d, _CharT __e)
+        : __string(__s), __delim(__d), __escape(__e) {}
 };
 
 template <class _CharT, class _Traits, class _Allocator>