diff --git a/Assets/VRM10/Runtime/Components/Vrm10Runtime/ControlRig/Rigs/ControlRigGenerationOption.cs b/Assets/VRM10/Runtime/Components/Vrm10Runtime/ControlRig/Rigs/ControlRigGenerationOption.cs
index eaae70332..b5a09268a 100644
--- a/Assets/VRM10/Runtime/Components/Vrm10Runtime/ControlRig/Rigs/ControlRigGenerationOption.cs
+++ b/Assets/VRM10/Runtime/Components/Vrm10Runtime/ControlRig/Rigs/ControlRigGenerationOption.cs
@@ -26,9 +26,9 @@ namespace UniVRM10
         Vrm0XCompatibleWithXR_EXT_hand_tracking = 2,
     }
 
-    public static class ControlRigGenerationOptionExtensions
+    internal static class ControlRigGenerationOptionExtensions
     {
-        public static IReadOnlyDictionary<HumanBodyBones, Quaternion> ToInitialRotations(this ControlRigGenerationOption option)
+        internal static IReadOnlyDictionary<HumanBodyBones, Quaternion> ToInitialRotations(this ControlRigGenerationOption option)
         {
             switch (option)
             {