diff --git a/Assets/VRM/UniJSON/Scripts/ConcreteCast.cs b/Assets/VRM/UniJSON/Scripts/ConcreteCast.cs
index 912cc2c37..1bbdd996d 100644
--- a/Assets/VRM/UniJSON/Scripts/ConcreteCast.cs
+++ b/Assets/VRM/UniJSON/Scripts/ConcreteCast.cs
@@ -2,6 +2,7 @@
 using System.IO;
 using System.Text;
 using UnityEngine;
+using System.Reflection;
 #if UNITY_EDITOR
 using UnityEditor;
 #endif
@@ -11,6 +12,19 @@ namespace UniJSON
 {
     public static partial class ConcreteCast
     {
+        public static string GetMethodName(Type src, Type dst)
+        {
+            return string.Format("Cast{0}To{1}", src.Name, dst.Name);
+        }
+
+        public static MethodInfo GetMethod(Type src, Type dst)
+        {
+            var name = GetMethodName(src, dst);
+            var mi = typeof(ConcreteCast).GetMethod(name, 
+                BindingFlags.Static | BindingFlags.Public);
+            return mi;
+        }
+
 #if UNITY_EDITOR
 
         static Type[] s_castTypes = new Type[]
@@ -47,11 +61,11 @@ namespace UniJSON {
                     foreach (var y in s_castTypes)
                     {
                         w.WriteLine(@"
-        public static $1 Cast$0To$1($0 src)
+        public static $1 $2($0 src)
         {
             return ($1)src;
         }
-".Replace("$0", x.Name).Replace("$1", y.Name));
+".Replace("$0", x.Name).Replace("$1", y.Name).Replace("$2", GetMethodName(x, y)));
                     }
                 }
                 w.WriteLine(@"
diff --git a/Assets/VRM/UniJSON/Scripts/GenericCast.cs b/Assets/VRM/UniJSON/Scripts/GenericCast.cs
index 69cb0219f..890172611 100644
--- a/Assets/VRM/UniJSON/Scripts/GenericCast.cs
+++ b/Assets/VRM/UniJSON/Scripts/GenericCast.cs
@@ -1,11 +1,4 @@
 using System;
-using System.IO;
-using System.Linq.Expressions;
-using System.Text;
-#if UNITY_EDITOR
-using UnityEditor;
-using UnityEngine;
-#endif
 
 
 namespace UniJSON
@@ -53,33 +46,30 @@ namespace UniJSON
     {
         public static Func<S, T> CreateCast<S, T>()
         {
-            if (typeof(S) == typeof(T))
+            var mi = ConcreteCast.GetMethod(typeof(S), typeof(T));
+            if (mi == null)
             {
-                // through
-                var src = Expression.Parameter(typeof(S), "src");
-                var lambda = Expression.Lambda(src, src);
-                return (Func<S, T>)lambda.Compile();
+                return (Func<S, T>)((S s) =>
+                {
+                    return (T)(object)s;
+                });
             }
             else
             {
-                // cast
-                var src = Expression.Parameter(typeof(S), "src");
-                var cast = Expression.Convert(src, typeof(T));
-                var lambda = Expression.Lambda(cast, src);
-                return (Func<S, T>)lambda.Compile();
+                return (Func<S, T>)((S s) =>
+                {
+                    return (T)mi.Invoke(null, new object[] { s });
+                });
             }
         }
 
         public static Func<S, Func<T>> CreateConst<S, T>()
         {
-            var src = Expression.Parameter(typeof(S), "src");
-            var convert = Expression.Convert(src, typeof(T));
-            var lambda = (Func<S, T>)Expression.Lambda(convert, src).Compile();
-            return s =>
+            var cast = CreateCast<S, T>();
+            return (Func<S, Func<T>>)((S s) =>
             {
-                var t = lambda(s);
-                return () => t;
-            };
+                return (Func<T>)(() => cast(s));
+            });
         }
     }
 }