diff --git a/Common/Cpp/Json/JsonTools.cpp b/Common/Cpp/Json/JsonTools.cpp
index 24313a92c7..b1cb5beccc 100644
--- a/Common/Cpp/Json/JsonTools.cpp
+++ b/Common/Cpp/Json/JsonTools.cpp
@@ -84,7 +84,7 @@ nlohmann::json to_nlohmann(const JsonValue& json){
         return ret;
     }
     if (json.is_object()){
-        nlohmann::json ret;
+        nlohmann::json::object_t ret;
         for (const auto& item : *json.to_object()){
             ret[item.first] = to_nlohmann(item.second);
         }
diff --git a/Common/Cpp/Json/JsonTools_Tests.cpp b/Common/Cpp/Json/JsonTools_Tests.cpp
new file mode 100644
index 0000000000..f548ac8a34
--- /dev/null
+++ b/Common/Cpp/Json/JsonTools_Tests.cpp
@@ -0,0 +1,77 @@
+/*  JSON Tools Tests
+ *
+ *  From: https://github.com/PokemonAutomation/
+ *
+ */
+
+#include <format>
+#include <string>
+#include <string_view>
+#include "Common/Cpp/TestRunners/UnitTestDatabase.h"
+#include "JsonValue.h"
+#include "JsonTools_Tests.h"
+
+namespace PokemonAutomation{
+namespace{
+
+
+
+struct DumpInput{
+    std::string_view name;
+    std::string_view text;
+};
+struct DumpExpectation{
+    std::string_view dumped;
+};
+struct DumpCase{
+    DumpInput input;
+    DumpExpectation expectation;
+};
+
+//  Empty containers must keep their type through dump() and parse_json().
+const DumpCase CASES[] = {
+    {.input = {.name = "Empty object", .text = "{}"}, .expectation = {.dumped = "{}"}},
+    {.input = {.name = "Nested empty object", .text = R"({"object":{}})"}, .expectation = {.dumped = R"({"object":{}})"}},
+    {.input = {.name = "Nested empty array", .text = R"({"array":[]})"}, .expectation = {.dumped = R"({"array":[]})"}},
+};
+
+
+
+class Test_JsonTools_DumpRoundTrip : public UnitTest{
+public:
+    explicit Test_JsonTools_DumpRoundTrip(DumpCase test)
+        : UnitTest(std::format("Common::JsonTools - {} round trip", test.input.name))
+        , m_test(test)
+    {}
+
+    virtual UnitTestResult run(Logger& logger, CancellableScope& scope) const override{
+        const std::string dumped = parse_json(std::string(m_test.input.text)).dump(-1);
+        if (dumped != m_test.expectation.dumped){
+            return UnitTestResult(std::format("dump: expected {}, got {}", m_test.expectation.dumped, dumped));
+        }
+        const std::string again = parse_json(dumped).dump(-1);
+        if (again != dumped){
+            return UnitTestResult(std::format("dump after reparse: expected {}, got {}", dumped, again));
+        }
+        return true;
+    }
+
+private:
+    DumpCase m_test;
+};
+
+
+
+} // namespace
+
+
+
+void add_tests_JsonTools(UnitTestDatabase& database){
+    for (const DumpCase& test : CASES){
+        database.add<Test_JsonTools_DumpRoundTrip>(test);
+    }
+}
+
+
+
+} // namespace PokemonAutomation
diff --git a/Common/Cpp/Json/JsonTools_Tests.h b/Common/Cpp/Json/JsonTools_Tests.h
new file mode 100644
index 0000000000..76d61d4b7c
--- /dev/null
+++ b/Common/Cpp/Json/JsonTools_Tests.h
@@ -0,0 +1,22 @@
+/*  JSON Tools Tests
+ *
+ *  From: https://github.com/PokemonAutomation/
+ *
+ */
+
+#ifndef PokemonAutomation_JsonTools_Tests_H
+#define PokemonAutomation_JsonTools_Tests_H
+
+#include "Common/Cpp/TestRunners/UnitTestDatabase.h"
+
+namespace PokemonAutomation{
+
+
+
+//  Register the JSON dump/parse round-trip tests.
+void add_tests_JsonTools(UnitTestDatabase& database);
+
+
+
+} // namespace PokemonAutomation
+#endif
diff --git a/SerialPrograms/Source/ComputerPrograms/ComputerPrograms_UnitTestRunner.cpp b/SerialPrograms/Source/ComputerPrograms/ComputerPrograms_UnitTestRunner.cpp
index 15fa65326b..73f475e5e2 100644
--- a/SerialPrograms/Source/ComputerPrograms/ComputerPrograms_UnitTestRunner.cpp
+++ b/SerialPrograms/Source/ComputerPrograms/ComputerPrograms_UnitTestRunner.cpp
@@ -4,6 +4,7 @@
  *
  */
 
+#include "Common/Cpp/Json/JsonTools_Tests.h"
 #include "Common/Cpp/ListenerSet.h"
 #include "Common/Cpp/MoveOnlyFunction_Tests.h"
 #include "Common/Cpp/ScopeExit.h"
@@ -58,6 +59,7 @@ UnitTestDatabase make_UNIT_TESTS_ALL(){
     add_tests_Sockets(ret, GlobalThreadPools::unlimited_normal());
     add_tests_BlackBorderDetector(ret);
     add_tests_ListenerSet(ret);
+    add_tests_JsonTools(ret);
     add_tests_MoveOnlyFunction(ret);
     SysbotBase::add_tests_SysbotBasePing(ret);
     SysbotBase::add_tests_SysbotBaseReceiveLine(ret);
diff --git a/SerialPrograms/cmake/SourceFiles.cmake b/SerialPrograms/cmake/SourceFiles.cmake
index 1ef2aaff87..8063bc387c 100644
--- a/SerialPrograms/cmake/SourceFiles.cmake
+++ b/SerialPrograms/cmake/SourceFiles.cmake
@@ -102,6 +102,8 @@ file(GLOB CORE_LIBRARY_SOURCES
     ../Common/Cpp/Json/JsonObject.h
     ../Common/Cpp/Json/JsonTools.cpp
     ../Common/Cpp/Json/JsonTools.h
+    ../Common/Cpp/Json/JsonTools_Tests.cpp
+    ../Common/Cpp/Json/JsonTools_Tests.h
     ../Common/Cpp/Json/JsonValue.cpp
     ../Common/Cpp/Json/JsonValue.h
     ../Common/Cpp/LifetimeSanitizer.cpp