diff --git a/.gitignore b/.gitignore
index 45682a7b..7b8ac004 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 *build*/
 cmake-build*/
+.raddbg_project
 .vscode/
 docs/
 .idea/
diff --git a/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.cpp b/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.cpp
index 5c5e72b8..0a250ced 100644
--- a/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.cpp
+++ b/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.cpp
@@ -13,13 +13,17 @@ inline ParamHolder::ParamHolder (ParamHolder* parent, std::string_view phName, b
               return OptionalPointer<ChainedArenaAllocator> { static_cast<size_t> (1024) };
           }(),
       },
+      allParamsMap { MapAllocator { arena } },
       name { arena::alloc_string (*arena, phName) },
       isOwning { phIsOwning }
 {
 }
 
 inline ParamHolder::ParamHolder (ChainedArenaAllocator& alloc, std::string_view phName, bool phIsOwning)
-    : arena { &alloc, false }, name { arena::alloc_string (*arena, phName) }, isOwning { phIsOwning }
+    : arena { &alloc, false },
+      allParamsMap { MapAllocator { arena } },
+      name { arena::alloc_string (*arena, phName) },
+      isOwning { phIsOwning }
 {
 }
 
@@ -110,6 +114,10 @@ std::enable_if_t<std::is_base_of_v<BoolParameter, ParamType>, void>
 template <typename... OtherParams>
 void ParamHolder::add (ParamHolder& paramHolder, OtherParams&... others)
 {
+    // This should be the parent of the holder being added.
+    // Maybe we can relax this restriction if we no longer need the allParamsMap.
+    jassert (arena == paramHolder.arena);
+
     allParamsMap.merge (paramHolder.allParamsMap);
     jassert (paramHolder.allParamsMap.empty()); // assuming no duplicate parameter IDs, all the parameters should be moved in the merge!
     things.insert (ThingPtr { reinterpret_cast<PackedVoid*> (&paramHolder), Holder });
diff --git a/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.h b/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.h
index 15edf2c2..bf696197 100644
--- a/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.h
+++ b/modules/plugin/chowdsp_plugin_state/Backend/chowdsp_ParamHolder.h
@@ -142,7 +142,8 @@ class ParamHolder
     using MapKey = std::string_view;
     using MapValue = ThingPtr;
     using MapAllocator = STLArenaAllocator<std::pair<const MapKey, MapValue>, ChainedArenaAllocator>;
-    std::unordered_map<MapKey, MapValue, std::hash<MapKey>, std::equal_to<>, MapAllocator> allParamsMap { MapAllocator { arena } };
+    using AllParamsMap = std::unordered_map<MapKey, MapValue, std::hash<MapKey>, std::equal_to<>, MapAllocator>;
+    AllParamsMap allParamsMap;
 
     std::string_view name;
     bool isOwning;
diff --git a/tests/plugin_tests/chowdsp_plugin_state_test/ParamHolderTest.cpp b/tests/plugin_tests/chowdsp_plugin_state_test/ParamHolderTest.cpp
index e9885e1a..a872c6ed 100644
--- a/tests/plugin_tests/chowdsp_plugin_state_test/ParamHolderTest.cpp
+++ b/tests/plugin_tests/chowdsp_plugin_state_test/ParamHolderTest.cpp
@@ -5,16 +5,17 @@ TEST_CASE ("ParamHolder Test", "[plugin][state]")
 {
     SECTION ("add()")
     {
-        chowdsp::BoolParameter::Ptr boolNested { "param1", "Param", false };
-        chowdsp::ChoiceParameter::Ptr choiceNested { "param2", "Param", juce::StringArray { "One", "Two" }, 0 };
-        chowdsp::ParamHolder nestedParams;
-        nestedParams.add (boolNested, choiceNested);
-
         chowdsp::ParamHolder params;
         std::array<chowdsp::PercentParameter::Ptr, 2> floatParams {
             chowdsp::PercentParameter::Ptr { "param3", "Param", 0.5f },
             chowdsp::PercentParameter::Ptr { "param4", "Param", 0.5f },
         };
+
+        chowdsp::BoolParameter::Ptr boolNested { "param1", "Param", false };
+        chowdsp::ChoiceParameter::Ptr choiceNested { "param2", "Param", juce::StringArray { "One", "Two" }, 0 };
+        chowdsp::ParamHolder nestedParams { &params };
+        nestedParams.add (boolNested, choiceNested);
+
         params.add (nestedParams, floatParams);
 
         auto allParamIDs = [&params]
diff --git a/tests/plugin_tests/chowdsp_plugin_state_test/StateSerializationTest.cpp b/tests/plugin_tests/chowdsp_plugin_state_test/StateSerializationTest.cpp
index 7b03c230..b2724573 100644
--- a/tests/plugin_tests/chowdsp_plugin_state_test/StateSerializationTest.cpp
+++ b/tests/plugin_tests/chowdsp_plugin_state_test/StateSerializationTest.cpp
@@ -116,7 +116,8 @@ using StateWithTripleOfSameType = chowdsp::PluginStateImpl<PluginParameterStateT
 
 struct NewGroup : chowdsp::ParamHolder
 {
-    NewGroup()
+    explicit NewGroup(ParamHolder* parent)
+        : ParamHolder { parent }
     {
         add (newParam);
     }
@@ -135,7 +136,7 @@ struct PluginParameterStateNewGroup : chowdsp::ParamHolder
     LevelParams levelParams { this };
     chowdsp::ChoiceParameter::Ptr mode { "mode", "Mode", juce::StringArray { "Percent", "Gain", "Percent / Gain", "Gain / Percent" }, 2 };
     chowdsp::BoolParameter::Ptr onOff { "on_off", "On/Off", true };
-    NewGroup newGroup;
+    NewGroup newGroup { this };
 };
 
 using StateWithNewGroup = chowdsp::PluginStateImpl<PluginParameterStateNewGroup>;