diff --git a/src/Neo.Extensions/UnsafeData.cs b/src/Neo.Extensions/UnsafeData.cs
index 6d4c9a6f8e..50126c25f4 100644
--- a/src/Neo.Extensions/UnsafeData.cs
+++ b/src/Neo.Extensions/UnsafeData.cs
@@ -18,14 +18,16 @@ public static class UnsafeData
         /// </summary>
         /// <param name="value">The length of the data.</param>
         /// <returns>The size of variable-length of the data.</returns>
-        public static int GetVarSize(int value)
+        public static byte GetVarSize(long value)
         {
             if (value < 0xFD)
                 return sizeof(byte);
-            else if (value <= 0xFFFF)
+            else if (value <= ushort.MaxValue)
                 return sizeof(byte) + sizeof(ushort);
-            else
+            else if (value <= uint.MaxValue)
                 return sizeof(byte) + sizeof(uint);
+            else
+                return sizeof(byte) + sizeof(ulong);
         }
     }
 }
diff --git a/tests/Neo.Extensions.Tests/UT_UnsafeData.cs b/tests/Neo.Extensions.Tests/UT_UnsafeData.cs
index 5c8bb310c3..98562fdfa2 100644
--- a/tests/Neo.Extensions.Tests/UT_UnsafeData.cs
+++ b/tests/Neo.Extensions.Tests/UT_UnsafeData.cs
@@ -12,22 +12,33 @@ public class UT_UnsafeData
         [TestMethod]
         public void TestGetVarSizeInt()
         {
-            for (int i = 0; i < 3; i++)
+            for (int i = 0; i < 4; i++)
             {
                 if (i == 0)
                 {
                     int result = UnsafeData.GetVarSize(1);
+                    int old = OldGetVarSize(1);
                     Assert.AreEqual(1, result);
+                    Assert.AreEqual(1, old);
                 }
                 else if (i == 1)
                 {
-                    int result = UnsafeData.GetVarSize(0xFFFF);
+                    int result = UnsafeData.GetVarSize(ushort.MaxValue);
+                    int old = OldGetVarSize(ushort.MaxValue);
                     Assert.AreEqual(3, result);
+                    Assert.AreEqual(3, old);
                 }
-                else
+                else if (i == 2)
                 {
-                    int result = UnsafeData.GetVarSize(0xFFFFFF);
+                    int result = UnsafeData.GetVarSize(uint.MaxValue);
+                    int old = OldGetVarSize(int.MaxValue);
                     Assert.AreEqual(5, result);
+                    Assert.AreEqual(5, old);
+                }
+                else
+                {
+                    int result = UnsafeData.GetVarSize(long.MaxValue);
+                    Assert.AreEqual(9, result);
                 }
             }
         }
@@ -159,5 +170,15 @@ enum TestEnum6 : long
         {
             case1 = 1, case2 = 2
         }
+
+        public static int OldGetVarSize(int value)
+        {
+            if (value < 0xFD)
+                return sizeof(byte);
+            else if (value <= ushort.MaxValue)
+                return sizeof(byte) + sizeof(ushort);
+            else
+                return sizeof(byte) + sizeof(uint);
+        }
     }
 }