diff --git a/neo.UnitTests/TestBlockchain.cs b/neo.UnitTests/TestBlockchain.cs
index 9e481e4e61..b3deab3039 100644
--- a/neo.UnitTests/TestBlockchain.cs
+++ b/neo.UnitTests/TestBlockchain.cs
@@ -52,6 +52,7 @@ public static NeoSystem InitializeMockNeoSystem()
                 mockStore.Setup(p => p.GetContracts()).Returns(new TestDataCache<UInt160, ContractState>());
                 mockStore.Setup(p => p.GetStorages()).Returns(new TestDataCache<StorageKey, StorageItem>());
                 mockStore.Setup(p => p.GetHeaderHashList()).Returns(new TestDataCache<UInt32Wrapper, HeaderHashList>());
+                mockStore.Setup(p => p.GetStateRoots()).Returns(new TestDataCache<UInt32Wrapper, StateRootState>());
                 mockStore.Setup(p => p.GetValidatorsCount()).Returns(new TestMetaDataCache<ValidatorsCountState>());
                 mockStore.Setup(p => p.GetBlockHashIndex()).Returns(new TestMetaDataCache<HashIndexState>());
                 mockStore.Setup(p => p.GetHeaderHashIndex()).Returns(new TestMetaDataCache<HashIndexState>());
diff --git a/neo/Network/P2P/Payloads/Transaction.cs b/neo/Network/P2P/Payloads/Transaction.cs
index 123fc3ba6e..d84cb909f6 100644
--- a/neo/Network/P2P/Payloads/Transaction.cs
+++ b/neo/Network/P2P/Payloads/Transaction.cs
@@ -82,24 +82,26 @@ public virtual Fixed8 NetworkFee
         }
 
         private IReadOnlyDictionary<CoinReference, TransactionOutput> _references;
+        private bool hasCalculatedReferences = false;
         public IReadOnlyDictionary<CoinReference, TransactionOutput> References
         {
             get
             {
-                if (_references == null)
+                if (!hasCalculatedReferences && _references == null)
                 {
+                    hasCalculatedReferences = true;
                     Dictionary<CoinReference, TransactionOutput> dictionary = new Dictionary<CoinReference, TransactionOutput>();
                     foreach (var group in Inputs.GroupBy(p => p.PrevHash))
                     {
                         Transaction tx = Blockchain.Singleton.Store.GetTransaction(group.Key);
                         if (tx == null) return null;
-                        foreach (var reference in group.Select(p => new
+                        foreach (var reference in group)
                         {
-                            Input = p,
-                            Output = tx.Outputs[p.PrevIndex]
-                        }))
-                        {
-                            dictionary.Add(reference.Input, reference.Output);
+                            if (reference.PrevIndex >= Outputs.Length)
+                            {
+                                return null;
+                            }
+                            dictionary.Add(reference, tx.Outputs[reference.PrevIndex]);
                         }
                     }
                     _references = dictionary;