diff --git a/src/UniTask/Assets/Plugins/UniTask/Runtime/IUniTaskSource.cs b/src/UniTask/Assets/Plugins/UniTask/Runtime/IUniTaskSource.cs
index 16a9bb3..17e3c88 100644
--- a/src/UniTask/Assets/Plugins/UniTask/Runtime/IUniTaskSource.cs
+++ b/src/UniTask/Assets/Plugins/UniTask/Runtime/IUniTaskSource.cs
@@ -19,7 +19,7 @@ namespace Cysharp.Threading.Tasks
 
     // similar as IValueTaskSource
     public interface IUniTaskSource
-#if !NETSTANDARD2_0
+#if (!UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER) && !NETSTANDARD2_0
         : System.Threading.Tasks.Sources.IValueTaskSource
 #pragma warning disable CS0108
 #endif
@@ -30,7 +30,7 @@ namespace Cysharp.Threading.Tasks
 
         UniTaskStatus UnsafeGetStatus(); // only for debug use.
 
-#if !NETSTANDARD2_0
+#if (!UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER) && !NETSTANDARD2_0
 #pragma warning restore CS0108
 
         System.Threading.Tasks.Sources.ValueTaskSourceStatus System.Threading.Tasks.Sources.IValueTaskSource.GetStatus(short token)
@@ -53,13 +53,13 @@ namespace Cysharp.Threading.Tasks
     }
 
     public interface IUniTaskSource<out T> : IUniTaskSource
-#if !NETSTANDARD2_0
+#if (!UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER) && !NETSTANDARD2_0
         , System.Threading.Tasks.Sources.IValueTaskSource<T>
 #endif
     {
         new T GetResult(short token);
 
-#if !NETSTANDARD2_0
+#if (!UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER) && !NETSTANDARD2_0
 
         new public UniTaskStatus GetStatus(short token)
         {
diff --git a/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.AsValueTask.cs b/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.AsValueTask.cs
index c3c4b7a..52db29a 100644
--- a/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.AsValueTask.cs
+++ b/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.AsValueTask.cs
@@ -1,4 +1,5 @@
-#pragma warning disable 0649
+#if !UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER
+#pragma warning disable 0649
 
 using System;
 using System.Threading.Tasks;
@@ -95,3 +96,4 @@ namespace Cysharp.Threading.Tasks
 #endif
     }
 }
+#endif
diff --git a/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.cs b/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.cs
index 13b81ef..348c196 100644
--- a/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.cs
+++ b/src/UniTask/Assets/Plugins/UniTask/Runtime/UniTask.cs
@@ -69,6 +69,8 @@ namespace Cysharp.Threading.Tasks
             return new UniTask<bool>(new IsCanceledSource(source), token);
         }
 
+#if !UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER
+
         public static implicit operator System.Threading.Tasks.ValueTask(in UniTask self)
         {
             if (self.source == null)
@@ -83,6 +85,8 @@ namespace Cysharp.Threading.Tasks
 #endif
         }
 
+#endif
+
         public override string ToString()
         {
             if (source == null) return "()";
@@ -436,6 +440,8 @@ namespace Cysharp.Threading.Tasks
             return self.AsUniTask();
         }
 
+#if !UNITY_2018_1_OR_NEWER || UNITY_2021_2_OR_NEWER
+
         public static implicit operator System.Threading.Tasks.ValueTask<T>(in UniTask<T> self)
         {
             if (self.source == null)
@@ -450,6 +456,8 @@ namespace Cysharp.Threading.Tasks
 #endif
         }
 
+#endif
+
         /// <summary>
         /// returns (bool IsCanceled, T Result) instead of throws OperationCanceledException.
         /// </summary>