diff --git a/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheExtensions.cs b/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheExtensions.cs
index 654d6139..846ac572 100644
--- a/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheExtensions.cs
+++ b/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheExtensions.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.Extensions.Caching.Memory;
@@ -24,21 +25,19 @@ public static bool Contains(this MemoryCache cache, object key)
 
         internal static void RegisterChild(this MemoryCache cache, object parentKey, object childKey)
         {
-            object temp;
-            if (cache.TryGetValue(parentKey, out temp))
+            if (cache.TryGetValue(parentKey, out var keys))
             {
-                var set = (HashSet<object>)temp;
-                set.Add(childKey);
+                var keySet = (ConcurrentDictionary<object, bool>)keys;
+                keySet.TryAdd(childKey, true);
             }
         }
 
         internal static void RemoveChilds(this MemoryCache cache, object region)
         {
-            object keys;
-            if (cache.TryGetValue(region, out keys))
+            if (cache.TryGetValue(region, out var keys))
             {
-                var keySet = (HashSet<object>)keys;
-                foreach (var key in keySet)
+                var keySet = (ConcurrentDictionary<object, bool>)keys;
+                foreach (var key in keySet.Keys)
                 {
                     cache.Remove(key);
                 }
diff --git a/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheHandle`1.cs b/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheHandle`1.cs
index dff819ce..248e4a7d 100644
--- a/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheHandle`1.cs
+++ b/src/CacheManager.Microsoft.Extensions.Caching.Memory/MemoryCacheHandle`1.cs
@@ -1,5 +1,5 @@
 using System;
-using System.Collections.Generic;
+using System.Collections.Concurrent;
 using CacheManager.Core;
 using CacheManager.Core.Internal;
 using CacheManager.Core.Logging;
@@ -227,7 +227,7 @@ private void CreateRegionToken(string region)
                 SlidingExpiration = TimeSpan.MaxValue,
             };
 
-            _cache.Set(region, new HashSet<object>(), options);
+            _cache.Set(region, new ConcurrentDictionary<object, bool>(), options);
         }
 
         private void ItemRemoved(object key, object value, EvictionReason reason, object state)