diff --git a/src/Neo/IO/Caching/KeyedCollectionSlim.cs b/src/Neo/IO/Caching/KeyedCollectionSlim.cs
new file mode 100644
index 0000000000..935faf36b2
--- /dev/null
+++ b/src/Neo/IO/Caching/KeyedCollectionSlim.cs
@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+
+namespace Neo.IO.Caching;
+
+abstract class KeyedCollectionSlim<TKey, TItem> where TKey : notnull
+{
+    private readonly LinkedList<TItem> _items = new();
+    private readonly Dictionary<TKey, LinkedListNode<TItem>> dict = new();
+
+    public int Count => dict.Count;
+    public TItem First => _items.First.Value;
+
+    protected abstract TKey GetKeyForItem(TItem item);
+
+    public void Add(TItem item)
+    {
+        var key = GetKeyForItem(item);
+        var node = _items.AddLast(item);
+        if (!dict.TryAdd(key, node))
+        {
+            _items.RemoveLast();
+            throw new ArgumentException("An element with the same key already exists in the collection.");
+        }
+    }
+
+    public bool Contains(TKey key) => dict.ContainsKey(key);
+
+    public void Remove(TKey key)
+    {
+        if (dict.Remove(key, out var node))
+            _items.Remove(node);
+    }
+
+    public void RemoveFirst()
+    {
+        var key = GetKeyForItem(_items.First.Value);
+        dict.Remove(key);
+        _items.RemoveFirst();
+    }
+}
diff --git a/src/Neo/Network/P2P/RemoteNode.ProtocolHandler.cs b/src/Neo/Network/P2P/RemoteNode.ProtocolHandler.cs
index ad6350a777..dfd21c63b8 100644
--- a/src/Neo/Network/P2P/RemoteNode.ProtocolHandler.cs
+++ b/src/Neo/Network/P2P/RemoteNode.ProtocolHandler.cs
@@ -19,7 +19,6 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Collections.ObjectModel;
 using System.Linq;
 using System.Net;
 
@@ -30,7 +29,7 @@ namespace Neo.Network.P2P
     partial class RemoteNode
     {
         private class Timer { }
-        private class PendingKnownHashesCollection : KeyedCollection<UInt256, (UInt256, DateTime)>
+        private class PendingKnownHashesCollection : KeyedCollectionSlim<UInt256, (UInt256, DateTime)>
         {
             protected override UInt256 GetKeyForItem((UInt256, DateTime) item)
             {
@@ -412,9 +411,9 @@ private void OnTimer()
             DateTime oneMinuteAgo = TimeProvider.Current.UtcNow.AddMinutes(-1);
             while (pendingKnownHashes.Count > 0)
             {
-                var (_, time) = pendingKnownHashes[0];
+                var (_, time) = pendingKnownHashes.First;
                 if (oneMinuteAgo <= time) break;
-                pendingKnownHashes.RemoveAt(0);
+                pendingKnownHashes.RemoveFirst();
             }
             if (oneMinuteAgo > lastSent)
                 EnqueueMessage(Message.Create(MessageCommand.Ping, PingPayload.Create(NativeContract.Ledger.CurrentIndex(system.StoreView))));