diff --git a/Assets/VRM10/Runtime/IO/Model/MeshImporter.cs b/Assets/VRM10/Runtime/IO/Model/MeshImporter.cs
index 94a5dc990..3e0c382e2 100644
--- a/Assets/VRM10/Runtime/IO/Model/MeshImporter.cs
+++ b/Assets/VRM10/Runtime/IO/Model/MeshImporter.cs
@@ -16,6 +16,10 @@ namespace UniVRM10
         {
             // submesh 方式
             var mesh = new UnityEngine.Mesh();
+            if (src.IndexBuffer.Count > UInt16.MaxValue)
+            {
+                mesh.indexFormat = UnityEngine.Rendering.IndexFormat.UInt32;
+            }
 
             mesh.vertices = src.VertexBuffer.Positions.GetSpan<Vector3>().ToArray();
             mesh.normals = src.VertexBuffer.Normals?.GetSpan<Vector3>().ToArray();
diff --git a/Assets/VRM10/Runtime/IO/Model/MeshImporterDivided.cs b/Assets/VRM10/Runtime/IO/Model/MeshImporterDivided.cs
index 4e9bd8b36..b2b108139 100644
--- a/Assets/VRM10/Runtime/IO/Model/MeshImporterDivided.cs
+++ b/Assets/VRM10/Runtime/IO/Model/MeshImporterDivided.cs
@@ -10,6 +10,10 @@ namespace UniVRM10
         public static UnityEngine.Mesh LoadDivided(VrmLib.MeshGroup src)
         {
             var dst = new UnityEngine.Mesh();
+            if (src.Meshes.Sum(x => x.IndexBuffer.Count) > ushort.MaxValue)
+            {
+                dst.indexFormat = UnityEngine.Rendering.IndexFormat.UInt32;
+            }
 
             //
             // vertices