Index: include/__hash_table
===================================================================
--- include/__hash_table
+++ include/__hash_table
@@ -100,6 +100,14 @@
     return size_t(1) << (std::numeric_limits<size_t>::digits - __clz(__n-1));
 }
 
+template <class _Pair, class _Key,
+          class _RawPair = typename __uncvref<_Pair>::type>
+struct __is_pair_with_key : false_type {};
+
+template <class _Pair, class _Key, class _First, class _Second>
+struct __is_pair_with_key<_Pair, _Key, pair<_First, _Second>>
+    : is_same<typename remove_const<_First>::type, _Key> {};
+
 template <class _Tp, class _Hash, class _Equal, class _Alloc> class __hash_table;
 
 template <class _NodePtr>      class _LIBCPP_TYPE_VIS_ONLY __hash_iterator;
@@ -901,6 +909,7 @@
 
     typedef typename _NodeTypes::__node_value_type           __node_value_type;
     typedef typename _NodeTypes::__container_value_type      __container_value_type;
+    typedef typename _NodeTypes::key_type                    key_type;
     typedef value_type&                              reference;
     typedef const value_type&                        const_reference;
     typedef typename __alloc_traits::pointer         pointer;
@@ -1039,13 +1048,41 @@
 
 #ifndef _LIBCPP_CXX03_LANG
     template <class _Key, class ..._Args>
+    _LIBCPP_INLINE_VISIBILITY
     pair<iterator, bool> __emplace_unique_key_args(_Key const& __k, _Args&&... __args);
 
     template <class... _Args>
-    pair<iterator, bool> __emplace_unique(_Args&&... __args);
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_unique_impl(_Args&&... __args);
+
+    template <class _Pp>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_unique(_Pp&& __x) {
+      return __emplace_unique_extract_key(_VSTD::forward<_Pp>(__x),
+                                          __is_pair_with_key<_Pp, key_type>());
+    }
     template <class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_unique(_Args&&... __args) {
+      return __emplace_unique_impl(_VSTD::forward<_Args>(__args)...);
+    }
+
+    template <class _Pp>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_unique_extract_key(_Pp&& __x, false_type) {
+      return __emplace_unique_impl(_VSTD::forward<_Pp>(__x));
+    }
+    template <class _Pp>
+    _LIBCPP_INLINE_VISIBILITY
+    pair<iterator, bool> __emplace_unique_extract_key(_Pp&& __x, true_type) {
+      return __emplace_unique_key_args(__x.first, _VSTD::forward<_Pp>(__x));
+    }
+
+    template <class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
     iterator __emplace_multi(_Args&&... __args);
     template <class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
     iterator __emplace_hint_multi(const_iterator __p, _Args&&... __args);
 
 
@@ -1987,7 +2024,7 @@
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 template <class... _Args>
 pair<typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator, bool>
-__hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_unique(_Args&&... __args)
+__hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_unique_impl(_Args&&... __args)
 {
     __node_holder __h = __construct_node(_VSTD::forward<_Args>(__args)...);
     pair<iterator, bool> __r = __node_insert_unique(__h.get());
Index: test/libcxx/containers/unord/unord.map/insert_dup_alloc.pass.cpp
===================================================================
--- /dev/null
+++ test/libcxx/containers/unord/unord.map/insert_dup_alloc.pass.cpp
@@ -0,0 +1,88 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// Check that we don't allocate when trying to insert a duplicate value into a
+// unordered_map.
+
+#include <cassert>
+#include <unordered_map>
+#include "count_new.hpp"
+#include "MoveOnly.h"
+
+int main() {
+  {
+    std::unordered_map<int, int> s;
+    assert(globalMemCounter.checkNewCalledEq(0));
+
+    for (int i = 0; i < 100; ++i) {
+      std::pair<const int, int> P(3, i);
+      s.insert(P);
+      s.insert(std::make_pair(3, i));
+      s.insert(std::make_pair(3, unsigned(i)));
+      s.insert(s.end(), std::make_pair(3, i));
+#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+      s.emplace(std::make_pair(3, i));
+      s.emplace_hint(s.end(), std::make_pair(3, i));
+#endif
+      {
+        const std::pair<int, int> P(3, i);
+        s.insert(P);
+#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+        s.emplace(P);
+        s.emplace_hint(s.end(), P);
+#endif
+      }
+    }
+
+    assert(s.size() == 1);
+    assert(s.count(3) == 1);
+    assert(s.at(3) == 0);
+    assert(globalMemCounter.checkNewCalledEq(2));
+  }
+  assert(globalMemCounter.checkOutstandingNewEq(0));
+  globalMemCounter.reset();
+#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+  {
+    std::unordered_map<MoveOnly, MoveOnly> s;
+    assert(globalMemCounter.checkNewCalledEq(0));
+
+    for (int i = 0; i < 100; i++) {
+      s.insert(std::make_pair(MoveOnly(3), MoveOnly(i)));
+      s.insert(s.end(), std::make_pair(MoveOnly(3), MoveOnly(i)));
+      s.emplace(std::make_pair(MoveOnly(3), MoveOnly(i)));
+      s.emplace_hint(s.end(), std::make_pair(MoveOnly(3), MoveOnly(i)));
+    }
+
+    assert(s.size() == 1);
+    assert(s.count(MoveOnly(3)) == 1);
+    assert(s.at(MoveOnly(3)) == 0);
+    assert(globalMemCounter.checkNewCalledEq(2));
+  }
+  assert(globalMemCounter.checkOutstandingNewEq(0));
+  globalMemCounter.reset();
+  {
+    std::unordered_map<int, MoveOnly> s;
+    assert(globalMemCounter.checkNewCalledEq(0));
+
+    for (int i = 0; i < 100; i++) {
+      s.insert(std::make_pair(3, MoveOnly(i)));
+      s.insert(s.end(), std::make_pair(3, MoveOnly(i)));
+      s.emplace(std::make_pair(3, MoveOnly(i)));
+      s.emplace_hint(s.end(), std::make_pair(3, MoveOnly(i)));
+    }
+
+    assert(s.size() == 1);
+    assert(s.count(3) == 1);
+    assert(s.at(3) == 0);
+    assert(globalMemCounter.checkNewCalledEq(2));
+  }
+  assert(globalMemCounter.checkOutstandingNewEq(0));
+  globalMemCounter.reset();
+#endif
+}