diff --git a/src/neo/Ledger/Blockchain.cs b/src/neo/Ledger/Blockchain.cs
index 74d06806e4..48c7da914a 100644
--- a/src/neo/Ledger/Blockchain.cs
+++ b/src/neo/Ledger/Blockchain.cs
@@ -429,7 +429,9 @@ private void OnParallelVerified(ParallelVerified parallelVerified)
             RelayResultReason reason = parallelVerified.VerifyResult;
             if (reason == RelayResultReason.Succeed)
             {
-                if (!MemPool.CanTransactionFitInPool(parallelVerified.Transaction))
+                if (View.ContainsTransaction(parallelVerified.Transaction.Hash))
+                    reason = RelayResultReason.AlreadyExists;
+                else if (!MemPool.CanTransactionFitInPool(parallelVerified.Transaction))
                     reason = RelayResultReason.OutOfMemory;
                 else if (!MemPool.TryAdd(parallelVerified.Transaction.Hash, parallelVerified.Transaction))
                     reason = RelayResultReason.OutOfMemory;