diff --git a/neo/Core/StorageKey.cs b/neo/Core/StorageKey.cs
index 3babef23c3..bb569a656c 100644
--- a/neo/Core/StorageKey.cs
+++ b/neo/Core/StorageKey.cs
@@ -11,12 +11,12 @@ public class StorageKey : IEquatable<StorageKey>, ISerializable
         public UInt160 ScriptHash;
         public byte[] Key;
 
-        int ISerializable.Size => ScriptHash.Size + Key.GetVarSize();
+        int ISerializable.Size => ScriptHash.Size + (Key.Length / 16 + 1) * 17;
 
         void ISerializable.Deserialize(BinaryReader reader)
         {
             ScriptHash = reader.ReadSerializable<UInt160>();
-            Key = reader.ReadVarBytes();
+            Key = reader.ReadBytesWithGrouping();
         }
 
         public bool Equals(StorageKey other)
@@ -43,7 +43,7 @@ public override int GetHashCode()
         void ISerializable.Serialize(BinaryWriter writer)
         {
             writer.Write(ScriptHash);
-            writer.WriteVarBytes(Key);
+            writer.WriteBytesWithGrouping(Key);
         }
     }
 }
diff --git a/neo/IO/Helper.cs b/neo/IO/Helper.cs
index 323db921d8..e264e443df 100644
--- a/neo/IO/Helper.cs
+++ b/neo/IO/Helper.cs
@@ -85,6 +85,26 @@ internal static int GetVarSize(this string value)
             return GetVarSize(size) + size;
         }
 
+        public static byte[] ReadBytesWithGrouping(this BinaryReader reader)
+        {
+            const int GROUP_SIZE = 16;
+            using (MemoryStream ms = new MemoryStream())
+            {
+                int padding = 0;
+                do
+                {
+                    byte[] group = reader.ReadBytes(GROUP_SIZE);
+                    padding = reader.ReadByte();
+                    if (padding > GROUP_SIZE)
+                        throw new FormatException();
+                    int count = GROUP_SIZE - padding;
+                    if (count > 0)
+                        ms.Write(group, 0, count);
+                } while (padding == 0);
+                return ms.ToArray();
+            }
+        }
+
         public static string ReadFixedString(this BinaryReader reader, int length)
         {
             byte[] data = reader.ReadBytes(length);
@@ -171,6 +191,26 @@ public static void Write<T>(this BinaryWriter writer, T[] value) where T : ISeri
             }
         }
 
+        public static void WriteBytesWithGrouping(this BinaryWriter writer, byte[] value)
+        {
+            const int GROUP_SIZE = 16;
+            int index = 0;
+            int remain = value.Length;
+            while (remain >= GROUP_SIZE)
+            {
+                writer.Write(value, index, GROUP_SIZE);
+                writer.Write((byte)0);
+                index += GROUP_SIZE;
+                remain -= GROUP_SIZE;
+            }
+            if (remain > 0)
+                writer.Write(value, index, remain);
+            int padding = GROUP_SIZE - remain;
+            for (int i = 0; i < padding; i++)
+                writer.Write((byte)0);
+            writer.Write((byte)padding);
+        }
+
         public static void WriteFixedString(this BinaryWriter writer, string value, int length)
         {
             if (value == null)
diff --git a/neo/Implementations/Blockchains/LevelDB/LevelDBBlockchain.cs b/neo/Implementations/Blockchains/LevelDB/LevelDBBlockchain.cs
index fc19773a37..0d356588aa 100644
--- a/neo/Implementations/Blockchains/LevelDB/LevelDBBlockchain.cs
+++ b/neo/Implementations/Blockchains/LevelDB/LevelDBBlockchain.cs
@@ -46,7 +46,7 @@ public LevelDBBlockchain(string path)
             Version version;
             Slice value;
             db = DB.Open(path, new Options { CreateIfMissing = true });
-            if (db.TryGet(ReadOptions.Default, SliceBuilder.Begin(DataEntryPrefix.SYS_Version), out value) && Version.TryParse(value.ToString(), out version) && version >= Version.Parse("2.6.0"))
+            if (db.TryGet(ReadOptions.Default, SliceBuilder.Begin(DataEntryPrefix.SYS_Version), out value) && Version.TryParse(value.ToString(), out version) && version >= Version.Parse("2.7.4"))
             {
                 ReadOptions options = new ReadOptions { FillCache = false };
                 value = db.Get(options, SliceBuilder.Begin(DataEntryPrefix.SYS_CurrentBlock));
diff --git a/neo/SmartContract/StateReader.cs b/neo/SmartContract/StateReader.cs
index 5ae79fc227..9eb99e26f2 100644
--- a/neo/SmartContract/StateReader.cs
+++ b/neo/SmartContract/StateReader.cs
@@ -948,8 +948,23 @@ protected virtual bool Storage_Find(ExecutionEngine engine)
                 StorageContext context = _interface.GetInterface<StorageContext>();
                 if (!CheckStorageContext(context)) return false;
                 byte[] prefix = engine.EvaluationStack.Pop().GetByteArray();
-                prefix = context.ScriptHash.ToArray().Concat(prefix).ToArray();
-                StorageIterator iterator = new StorageIterator(Storages.Find(prefix).GetEnumerator());
+                byte[] prefix_key;
+                using (MemoryStream ms = new MemoryStream())
+                {
+                    int index = 0;
+                    int remain = prefix.Length;
+                    while (remain >= 16)
+                    {
+                        ms.Write(prefix, index, 16);
+                        ms.WriteByte(0);
+                        index += 16;
+                        remain -= 16;
+                    }
+                    if (remain > 0)
+                        ms.Write(prefix, index, remain);
+                    prefix_key = context.ScriptHash.ToArray().Concat(ms.ToArray()).ToArray();
+                }
+                StorageIterator iterator = new StorageIterator(Storages.Find(prefix_key).Where(p => p.Key.Key.Take(prefix.Length).SequenceEqual(prefix)).GetEnumerator());
                 engine.EvaluationStack.Push(StackItem.FromInterface(iterator));
                 disposables.Add(iterator);
                 return true;
diff --git a/neo/neo.csproj b/neo/neo.csproj
index e286042071..b73763d434 100644
--- a/neo/neo.csproj
+++ b/neo/neo.csproj
@@ -3,7 +3,7 @@
   <PropertyGroup>
     <Copyright>2015-2017 The Neo Project</Copyright>
     <AssemblyTitle>Neo</AssemblyTitle>
-    <Version>2.7.3</Version>
+    <Version>2.7.4</Version>
     <Authors>The Neo Project</Authors>
     <TargetFrameworks>netstandard2.0;net47</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>