diff --git a/TUnit.Mocks/MockEngine.cs b/TUnit.Mocks/MockEngine.cs
index bdeefe6f50..b431cd82ab 100644
--- a/TUnit.Mocks/MockEngine.cs
+++ b/TUnit.Mocks/MockEngine.cs
@@ -4,6 +4,7 @@
 using TUnit.Mocks.Setup.Behaviors;
 using TUnit.Mocks.Verification;
 using System.Collections.Concurrent;
+using System.Threading;
 using System.ComponentModel;
 
 namespace TUnit.Mocks;
@@ -24,11 +25,12 @@ public sealed class MockEngine<T> : IMockEngineAccess where T : class
     private readonly Dictionary<int, List<MethodSetup>> _setupsByMember = new();
     private readonly Lock _setupLock = new();
     private readonly ConcurrentQueue<CallRecord> _callHistory = new();
-    private readonly ConcurrentDictionary<string, object?> _autoTrackValues = new();
-    private readonly ConcurrentQueue<(string EventName, bool IsSubscribe)> _eventSubscriptions = new();
-    private readonly ConcurrentDictionary<string, Action> _onSubscribeCallbacks = new();
-    private readonly ConcurrentDictionary<string, Action> _onUnsubscribeCallbacks = new();
-    private readonly ConcurrentDictionary<string, IMock?> _autoMockCache = new();
+
+    private ConcurrentDictionary<string, object?>? _autoTrackValues;
+    private ConcurrentQueue<(string EventName, bool IsSubscribe)>? _eventSubscriptions;
+    private ConcurrentDictionary<string, Action>? _onSubscribeCallbacks;
+    private ConcurrentDictionary<string, Action>? _onUnsubscribeCallbacks;
+    private ConcurrentDictionary<string, IMock?>? _autoMockCache;
 
     /// <summary>
     /// The current state name for state machine mocking. Null means no state (all setups match).
@@ -77,6 +79,21 @@ public MockEngine(MockBehavior behavior)
         Behavior = behavior;
     }
 
+    private ConcurrentDictionary<string, object?> AutoTrackValues
+        => LazyInitializer.EnsureInitialized(ref _autoTrackValues)!;
+
+    private ConcurrentQueue<(string EventName, bool IsSubscribe)> EventSubscriptions
+        => LazyInitializer.EnsureInitialized(ref _eventSubscriptions)!;
+
+    private ConcurrentDictionary<string, Action> OnSubscribeCallbacks
+        => LazyInitializer.EnsureInitialized(ref _onSubscribeCallbacks)!;
+
+    private ConcurrentDictionary<string, Action> OnUnsubscribeCallbacks
+        => LazyInitializer.EnsureInitialized(ref _onUnsubscribeCallbacks)!;
+
+    private ConcurrentDictionary<string, IMock?> AutoMockCache
+        => LazyInitializer.EnsureInitialized(ref _autoMockCache)!;
+
     /// <summary>
     /// Transitions the engine to the specified state. Null clears the state.
     /// </summary>
@@ -125,7 +142,7 @@ public void HandleCall(int memberId, string memberName, object?[] args)
         // Auto-track property setters: store value keyed by property name
         if (AutoTrackProperties && memberName.StartsWith("set_", StringComparison.Ordinal) && args.Length > 0)
         {
-            _autoTrackValues[memberName.Substring(4)] = args[0];
+            AutoTrackValues[memberName[4..]] = args[0];
         }
 
         var (setupFound, behavior, matchedSetup) = FindMatchingSetup(memberId, args);
@@ -211,9 +228,9 @@ public TReturn HandleCallWithReturn<TReturn>(int memberId, string memberName, ob
         callRecord.IsUnmatched = true;
 
         // Auto-track property getters: return stored value if available
-        if (AutoTrackProperties && memberName.StartsWith("get_", StringComparison.Ordinal))
+        if (AutoTrackProperties && Volatile.Read(ref _autoTrackValues) is { } trackValues && memberName.StartsWith("get_", StringComparison.Ordinal))
         {
-            if (_autoTrackValues.TryGetValue(memberName.Substring(4), out var trackedValue))
+            if (trackValues.TryGetValue(memberName[4..], out var trackedValue))
             {
                 if (trackedValue is TReturn typed) return typed;
                 if (trackedValue is null) return default(TReturn)!;
@@ -236,7 +253,7 @@ public TReturn HandleCallWithReturn<TReturn>(int memberId, string memberName, ob
         if (Behavior == MockBehavior.Loose && typeof(TReturn).IsInterface)
         {
             var cacheKey = memberName + "|" + typeof(TReturn).FullName;
-            var autoMock = _autoMockCache.GetOrAdd(cacheKey, _ =>
+            var autoMock = AutoMockCache.GetOrAdd(cacheKey, _ =>
             {
                 Mock.TryCreateAutoMock(typeof(TReturn), Behavior, out var m);
                 return m;
@@ -465,7 +482,12 @@ public Diagnostics.MockDiagnostics GetDiagnostics()
     [EditorBrowsable(EditorBrowsableState.Never)]
     public bool TryGetAutoMock(string cacheKey, [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] out IMock? mock)
     {
-        return _autoMockCache.TryGetValue(cacheKey, out mock);
+        if (Volatile.Read(ref _autoMockCache) is not { } cache)
+        {
+            mock = null;
+            return false;
+        }
+        return cache.TryGetValue(cacheKey, out mock);
     }
 
     /// <summary>
@@ -483,11 +505,11 @@ public void Reset()
         // Drain the queue
         while (_callHistory.TryDequeue(out _)) { }
 
-        _autoTrackValues.Clear();
-        while (_eventSubscriptions.TryDequeue(out _)) { }
-        _onSubscribeCallbacks.Clear();
-        _onUnsubscribeCallbacks.Clear();
-        _autoMockCache.Clear();
+        Volatile.Write(ref _autoTrackValues, null);
+        Volatile.Write(ref _eventSubscriptions, null);
+        Volatile.Write(ref _onSubscribeCallbacks, null);
+        Volatile.Write(ref _onUnsubscribeCallbacks, null);
+        Volatile.Write(ref _autoMockCache, null);
     }
 
     /// <summary>
@@ -496,7 +518,7 @@ public void Reset()
     [EditorBrowsable(EditorBrowsableState.Never)]
     public void OnSubscribe(string eventName, Action callback)
     {
-        _onSubscribeCallbacks[eventName] = callback;
+        OnSubscribeCallbacks[eventName] = callback;
     }
 
     /// <summary>
@@ -505,7 +527,7 @@ public void OnSubscribe(string eventName, Action callback)
     [EditorBrowsable(EditorBrowsableState.Never)]
     public void OnUnsubscribe(string eventName, Action callback)
     {
-        _onUnsubscribeCallbacks[eventName] = callback;
+        OnUnsubscribeCallbacks[eventName] = callback;
     }
 
     /// <summary>
@@ -514,18 +536,18 @@ public void OnUnsubscribe(string eventName, Action callback)
     [EditorBrowsable(EditorBrowsableState.Never)]
     public void RecordEventSubscription(string eventName, bool isSubscribe)
     {
-        _eventSubscriptions.Enqueue((eventName, isSubscribe));
+        EventSubscriptions.Enqueue((eventName, isSubscribe));
 
         if (isSubscribe)
         {
-            if (_onSubscribeCallbacks.TryGetValue(eventName, out var callback))
+            if (Volatile.Read(ref _onSubscribeCallbacks) is { } subCallbacks && subCallbacks.TryGetValue(eventName, out var callback))
             {
                 callback();
             }
         }
         else
         {
-            if (_onUnsubscribeCallbacks.TryGetValue(eventName, out var callback))
+            if (Volatile.Read(ref _onUnsubscribeCallbacks) is { } unsubCallbacks && unsubCallbacks.TryGetValue(eventName, out var callback))
             {
                 callback();
             }
@@ -538,8 +560,9 @@ public void RecordEventSubscription(string eventName, bool isSubscribe)
     [EditorBrowsable(EditorBrowsableState.Never)]
     public int GetEventSubscriberCount(string eventName)
     {
+        if (Volatile.Read(ref _eventSubscriptions) is not { } subs) return 0;
         int count = 0;
-        foreach (var (name, isSub) in _eventSubscriptions)
+        foreach (var (name, isSub) in subs)
         {
             if (name == eventName)
             {
@@ -555,7 +578,8 @@ public int GetEventSubscriberCount(string eventName)
     [EditorBrowsable(EditorBrowsableState.Never)]
     public bool WasEventSubscribed(string eventName)
     {
-        foreach (var (name, isSub) in _eventSubscriptions)
+        if (Volatile.Read(ref _eventSubscriptions) is not { } subs) return false;
+        foreach (var (name, isSub) in subs)
         {
             if (name == eventName && isSub) return true;
         }