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diff --git a/json4cpp/tests/src/unit-ordered_json.cpp b/json4cpp/tests/src/unit-ordered_json.cpp
new file mode 100644
index 0000000000..10bb037bc8
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+++ b/json4cpp/tests/src/unit-ordered_json.cpp
@@ -0,0 +1,71 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#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}");
+
+    // remove again and nothing changes
+    j.erase("element1");
+    oj.erase("element1");
+
+    CHECK(j.dump() == "{\"element2\":2,\"element3\":3}");
+    CHECK(oj.dump() == "{\"element3\":3,\"element2\":2}");
+
+    // There are no dup keys cause constructor calls emplace...
+    json const multi {{"z", 1}, {"m", 2}, {"m", 3}, {"y", 4}, {"m", 5}};
+    CHECK(multi.size() == 3);
+    CHECK(multi.dump() == "{\"m\":2,\"y\":4,\"z\":1}");
+
+    ordered_json multi_ordered {{"z", 1}, {"m", 2}, {"m", 3}, {"y", 4}, {"m", 5}};
+    CHECK(multi_ordered.size() == 3);
+    CHECK(multi_ordered.dump() == "{\"z\":1,\"m\":2,\"y\":4}");
+    CHECK(multi_ordered.erase("m") == 1);
+    CHECK(multi_ordered.dump() == "{\"z\":1,\"y\":4}");
+
+    // Ranged insert test.
+    // It seems that values shouldn't be overwritten. Only new values are added
+    json j1 {{"c", 1}, {"b", 2}, {"a", 3}};
+    const json j2 {{"c", 77}, {"d", 42}, {"a", 4}};
+    j1.insert( j2.cbegin(), j2.cend() );
+    CHECK(j1.size() == 4);
+    CHECK(j1.dump() == "{\"a\":3,\"b\":2,\"c\":1,\"d\":42}");
+
+    ordered_json oj1 {{"c", 1}, {"b", 2}, {"a", 3}};
+    const ordered_json oj2 {{"c", 77}, {"d", 42}, {"a", 4}};
+    oj1.insert( oj2.cbegin(), oj2.cend() );
+    CHECK(oj1.size() == 4);
+    CHECK(oj1.dump() == "{\"c\":1,\"b\":2,\"a\":3,\"d\":42}");
+}