diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/FileSystemStorage.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/FileSystemStorage.cs
index 2ffb85872..61208db1e 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/FileSystemStorage.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/FileSystemStorage.cs
@@ -69,7 +69,7 @@ namespace UniGLTF
     /// <summary>
     /// for UnitTest
     /// </summary>
-    public class GltfStorage : IStorage
+    public sealed class GltfStorage : IStorage
     {
         glTF _gltf;