diff --git a/include/nlohmann/json.hpp b/include/nlohmann/json.hpp
index 409a6e79..15921726 100644
--- a/include/nlohmann/json.hpp
+++ b/include/nlohmann/json.hpp
@@ -72,6 +72,7 @@ SOFTWARE.
#include <nlohmann/detail/output/serializer.hpp>
#include <nlohmann/detail/value_t.hpp>
#include <nlohmann/json_fwd.hpp>
+#include <nlohmann/ordered_map.hpp>
/*!
@brief namespace for Niels Lohmann
diff --git a/include/nlohmann/json_fwd.hpp b/include/nlohmann/json_fwd.hpp
index 824e86a1..d9e5428d 100644
--- a/include/nlohmann/json_fwd.hpp
+++ b/include/nlohmann/json_fwd.hpp
@@ -60,6 +60,19 @@ uses the standard template types.
@since version 1.0.0
*/
using json = basic_json<>;
+
+template<class Key, class T, class IgnoredLess, class Allocator, class Container>
+struct ordered_map;
+
+/*!
+@brief ordered JSON class
+
+This type preserves the insertion order of object keys.
+
+@since version 3.9.0
+*/
+using ordered_json = basic_json<nlohmann::ordered_map>;
+
} // namespace nlohmann
#endif // INCLUDE_NLOHMANN_JSON_FWD_HPP_
diff --git a/include/nlohmann/ordered_map.hpp b/include/nlohmann/ordered_map.hpp
new file mode 100644
index 00000000..744541f3
--- /dev/null
+++ b/include/nlohmann/ordered_map.hpp
@@ -0,0 +1,62 @@
+#pragma once
+
+#include <functional> // less
+#include <memory> // allocator
+#include <utility> // pair
+#include <vector> // vector
+
+namespace nlohmann
+{
+
+/// ordered_map: a minimal map-like container that preserves insertion order
+/// for use within nlohmann::basic_json<ordered_map>
+template<class Key, class T, class IgnoredLess = std::less<Key>,
+ class Allocator = std::allocator<std::pair<const Key, T>>,
+ class Container = std::vector<std::pair<const Key, T>, Allocator>>
+struct ordered_map : Container
+{
+ using key_type = Key;
+ using mapped_type = T;
+ using value_type = std::pair<const Key, T>;
+ using Container::Container;
+
+ std::pair<typename Container::iterator, bool> emplace(key_type&& key, T&& t)
+ {
+ for (auto it = this->begin(); it != this->end(); ++it)
+ {
+ if (it->first == key)
+ {
+ return {it, false};
+ }
+ }
+
+ this->emplace_back(key, t);
+ return {--this->end(), true};
+ }
+
+ std::size_t erase(const key_type& key)
+ {
+ std::size_t result = 0;
+ for (auto it = this->begin(); it != this->end();)
+ {
+ if (it->first == key)
+ {
+ ++result;
+ it = Container::erase(it);
+ }
+ else
+ {
+ ++it;
+ }
+ }
+
+ return result;
+ }
+
+ T& operator[](key_type&& key)
+ {
+ return emplace(std::move(key), T{}).first->second;
+ }
+};
+
+} // namespace nlohmann
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index cc822a54..f7f1664e 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -2772,6 +2772,15 @@ uses the standard template types.
@since version 1.0.0
*/
using json = basic_json<>;
+
+template<class Key, class T, class IgnoredLess, class Allocator, class Container>
+struct ordered_map;
+
+/*!
+@since version 3.9.0
+*/
+using ordered_json = basic_json<nlohmann::ordered_map>;
+
} // namespace nlohmann
#endif // INCLUDE_NLOHMANN_JSON_FWD_HPP_
@@ -15853,6 +15862,70 @@ class serializer
// #include <nlohmann/json_fwd.hpp>
+// #include <nlohmann/ordered_map.hpp>
+
+
+#include <functional> // less
+#include <memory> // allocator
+#include <utility> // pair
+#include <vector> // vector
+
+namespace nlohmann
+{
+
+/// ordered_map: a minimal map-like container that preserves insertion order
+/// for use within nlohmann::basic_json<ordered_map>
+template<class Key, class T, class IgnoredLess = std::less<Key>,
+ class Allocator = std::allocator<std::pair<const Key, T>>,
+ class Container = std::vector<std::pair<const Key, T>, Allocator>>
+struct ordered_map : Container
+{
+ using key_type = Key;
+ using mapped_type = T;
+ using value_type = std::pair<const Key, T>;
+ using Container::Container;
+
+ std::pair<typename Container::iterator, bool> emplace(Key&& key, T&& t)
+ {
+ for (auto it = this->begin(); it != this->end(); ++it)
+ {
+ if (it->first == key)
+ {
+ return {it, false};
+ }
+ }
+
+ this->emplace_back(key, t);
+ return {--this->end(), true};
+ }
+
+ std::size_t erase(const Key& key)
+ {
+ std::size_t result = 0;
+ for (auto it = this->begin(); it != this->end(); )
+ {
+ if (it->first == key)
+ {
+ ++result;
+ it = Container::erase(it);
+ }
+ else
+ {
+ ++it;
+ }
+ }
+
+ return result;
+ }
+
+ T& operator[]( Key&& key )
+ {
+ return emplace(std::move(key), T{}).first->second;
+ }
+};
+
+} // namespace nlohmann
+
/*!
@brief namespace for Niels Lohmann
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index fdf5ac5b..8e663f49 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -123,6 +123,7 @@ set(files
src/unit-modifiers.cpp
src/unit-msgpack.cpp
src/unit-noexcept.cpp
+ src/unit-ordered_json.cpp
src/unit-pointer_access.cpp
src/unit-readme.cpp
src/unit-reference_access.cpp
diff --git a/test/src/unit-ordered_json.cpp b/test/src/unit-ordered_json.cpp
new file mode 100644
index 00000000..1a97ece6
--- /dev/null
+++ b/test/src/unit-ordered_json.cpp
@@ -0,0 +1,61 @@
+/*
+ __ _____ _____ _____
+ __| | __| | | | JSON for Modern C++ (test suite)
+| | |__ | | | | | | version 3.8.0
+|_____|_____|_____|_|___| https://github.com/nlohmann/json
+
+Licensed under the MIT License <http://opensource.org/licenses/MIT>.
+SPDX-License-Identifier: MIT
+Copyright (c) 2013-2019 Niels Lohmann <http://nlohmann.me>.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+
+
+TEST_CASE("ordered_json")
+{
+ json j;
+ ordered_json oj;
+
+ j["element3"] = 3;
+ j["element1"] = 1;
+ j["element2"] = 2;
+
+ oj["element3"] = 3;
+ oj["element1"] = 1;
+ oj["element2"] = 2;
+
+ CHECK(j.dump() == "{\"element1\":1,\"element2\":2,\"element3\":3}");
+ CHECK(oj.dump() == "{\"element3\":3,\"element1\":1,\"element2\":2}");
+
+ CHECK(j == json(oj));
+ CHECK(ordered_json(json(oj)) == ordered_json(j));
+
+ j.erase("element1");
+ oj.erase("element1");
+
+ CHECK(j.dump() == "{\"element2\":2,\"element3\":3}");
+ CHECK(oj.dump() == "{\"element3\":3,\"element2\":2}");
+}