diff --git a/libcxx/include/__bit_reference b/libcxx/include/__bit_reference
--- a/libcxx/include/__bit_reference
+++ b/libcxx/include/__bit_reference
@@ -47,6 +47,10 @@
     friend class __bit_const_reference<_Cp>;
     friend class __bit_iterator<_Cp, false>;
 public:
+    _LIBCPP_INLINE_VISIBILITY
+    __bit_reference(const __bit_reference& __x) _NOEXCEPT : __seg_(__x.__seg_),
+                                                            __mask_(__x.__mask_) {}
+
     _LIBCPP_INLINE_VISIBILITY operator bool() const _NOEXCEPT
         {return static_cast<bool>(*__seg_ & __mask_);}
     _LIBCPP_INLINE_VISIBILITY bool operator ~() const _NOEXCEPT
@@ -146,8 +150,6 @@
     _LIBCPP_CONSTEXPR
     __bit_const_reference(__storage_pointer __s, __storage_type __m) _NOEXCEPT
         : __seg_(__s), __mask_(__m) {}
-
-    __bit_const_reference& operator=(const __bit_const_reference& __x);
 };
 
 // find