diff --git a/Assets/VRM10/vrmlib/Runtime/VertexBuffer.cs b/Assets/VRM10/vrmlib/Runtime/VertexBuffer.cs
index c6b74351d..268ca7326 100644
--- a/Assets/VRM10/vrmlib/Runtime/VertexBuffer.cs
+++ b/Assets/VRM10/vrmlib/Runtime/VertexBuffer.cs
@@ -27,7 +27,8 @@ namespace VrmLib
 
         public void Add(string key, BufferAccessor accessor)
         {
-            VertexBuffers.Add(key, accessor);
+            // if exists, over write
+            VertexBuffers[key] = accessor;
         }
 
         public bool TryGetValue(string key, out BufferAccessor accessor)