diff --git a/src/metldata/builtin_transformations/infer_relations/model_transform.py b/src/metldata/builtin_transformations/infer_relations/model_transform.py
index 202145e..41c9efa 100644
--- a/src/metldata/builtin_transformations/infer_relations/model_transform.py
+++ b/src/metldata/builtin_transformations/infer_relations/model_transform.py
@@ -160,5 +160,5 @@ def add_inferred_relations(
         )
 
     model_dict = model.model_dump()
-    model_dict.update({"classes": {**model.classes, **updated_class_defs}})
+    model_dict["classes"].update(updated_class_defs)
     return SchemaPack.model_validate(model_dict)