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diff --git a/json4cpp/tests/src/fuzzer-parse_ubjson.cpp b/json4cpp/tests/src/fuzzer-parse_ubjson.cpp
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+++ b/json4cpp/tests/src/fuzzer-parse_ubjson.cpp
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+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  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
+
+/*
+This file implements a parser test suitable for fuzz testing. Given a byte
+array data, it performs the following steps:
+
+- j1 = from_ubjson(data)
+- vec = to_ubjson(j1)
+- j2 = from_ubjson(vec)
+- assert(j1 == j2)
+- vec2 = to_ubjson(j1, use_size = true, use_type = false)
+- j3 = from_ubjson(vec2)
+- assert(j1 == j3)
+- vec3 = to_ubjson(j1, use_size = true, use_type = true)
+- j4 = from_ubjson(vec3)
+- assert(j1 == j4)
+
+The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
+drivers.
+*/
+
+#include <iostream>
+#include <sstream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+// see http://llvm.org/docs/LibFuzzer.html
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    try
+    {
+        // step 1: parse input
+        std::vector<uint8_t> const vec1(data, data + size);
+        json const j1 = json::from_ubjson(vec1);
+
+        try
+        {
+            // step 2.1: round trip without adding size annotations to container types
+            std::vector<uint8_t> const vec2 = json::to_ubjson(j1, false, false);
+
+            // step 2.2: round trip with adding size annotations but without adding type annotations to container types
+            std::vector<uint8_t> const vec3 = json::to_ubjson(j1, true, false);
+
+            // step 2.3: round trip with adding size as well as type annotations to container types
+            std::vector<uint8_t> const vec4 = json::to_ubjson(j1, true, true);
+
+            // parse serialization
+            json const j2 = json::from_ubjson(vec2);
+            json const j3 = json::from_ubjson(vec3);
+            json const j4 = json::from_ubjson(vec4);
+
+            // serializations must match
+            assert(json::to_ubjson(j2, false, false) == vec2);
+            assert(json::to_ubjson(j3, true, false) == vec3);
+            assert(json::to_ubjson(j4, true, true) == vec4);
+        }
+        catch (const json::parse_error&)
+        {
+            // parsing a UBJSON serialization must not fail
+            assert(false);
+        }
+    }
+    catch (const json::parse_error&)
+    {
+        // parse errors are ok, because input may be random bytes
+    }
+    catch (const json::type_error&)
+    {
+        // type errors can occur during parsing, too
+    }
+    catch (const json::out_of_range&)
+    {
+        // out of range errors may happen if provided sizes are excessive
+    }
+
+    // return 0 - non-zero return values are reserved for future use
+    return 0;
+}