diff --git a/Editor/Processors/InitializeAnimatorOptimizer.cs b/Editor/Processors/InitializeAnimatorOptimizer.cs
index de879372b..8444e4065 100644
--- a/Editor/Processors/InitializeAnimatorOptimizer.cs
+++ b/Editor/Processors/InitializeAnimatorOptimizer.cs
@@ -1,3 +1,5 @@
+#if UNITY_2021_3_OR_NEWER
+
 using System;
 using System.Collections.Generic;
 using Anatawa12.AvatarOptimizer.Processors.TraceAndOptimizes;
@@ -176,3 +178,5 @@ protected override ComponentSupport GetComponentSupport(Object o)
         }
     }
 }
+
+#endif