diff --git a/Assets/VRM10/Runtime/Migration/MigrationMToon.cs b/Assets/VRM10/Runtime/Migration/MigrationMToon.cs
index 2b26ef613..821df947d 100644
--- a/Assets/VRM10/Runtime/Migration/MigrationMToon.cs
+++ b/Assets/VRM10/Runtime/Migration/MigrationMToon.cs
@@ -375,7 +375,10 @@ namespace UniVRM10
                         gltfMaterial.alphaMode = "BLEND";
                         dst.TransparentWithZWrite = true;
                         gltfMaterial.alphaCutoff = 0.5f;
-                        dst.RenderQueueOffsetNumber = Mathf.Clamp(transparentRenderQueueMap[mtoon.Definition.Rendering.RenderQueueOffsetNumber], 0, +9);
+                        if (transparentRenderQueueMap.TryGetValue(mtoon.Definition.Rendering.RenderQueueOffsetNumber, out int value))
+                        {
+                            dst.RenderQueueOffsetNumber = Mathf.Clamp(value, 0, +9);
+                        }
                         break;
                     default:
                         throw new ArgumentOutOfRangeException();