diff --git a/src/neo/Ledger/Blockchain.cs b/src/neo/Ledger/Blockchain.cs
index 4418e461d8..b5af18af84 100644
--- a/src/neo/Ledger/Blockchain.cs
+++ b/src/neo/Ledger/Blockchain.cs
@@ -13,6 +13,7 @@
 using Neo.SmartContract.Native;
 using Neo.VM;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -62,7 +63,7 @@ public class RelayResult { public IInventory Inventory; public VerifyResult Resu
         private readonly IActorRef txrouter;
         private readonly List<UInt256> header_index = new List<UInt256>();
         private uint stored_header_count = 0;
-        private readonly Dictionary<UInt256, Block> block_cache = new Dictionary<UInt256, Block>();
+        private readonly ConcurrentDictionary<UInt256, Block> block_cache = new ConcurrentDictionary<UInt256, Block>();
         private readonly Dictionary<uint, UnverifiedBlocksList> block_cache_unverified = new Dictionary<uint, UnverifiedBlocksList>();
         internal readonly RelayCache RelayCache = new RelayCache(100);
         private SnapshotView currentSnapshot;
@@ -509,7 +510,7 @@ private void Persist(Block block)
                 if (commitExceptions != null) throw new AggregateException(commitExceptions);
             }
             UpdateCurrentSnapshot();
-            block_cache.Remove(block.PrevHash);
+            block_cache.TryRemove(block.PrevHash, out _);
             MemPool.UpdatePoolForBlockPersisted(block, currentSnapshot);
             Context.System.EventStream.Publish(new PersistCompleted { Block = block });
         }