diff --git a/src/py/mat3ra/made/tools/build/defect/builders.py b/src/py/mat3ra/made/tools/build/defect/builders.py
index ad04182e..d430724c 100644
--- a/src/py/mat3ra/made/tools/build/defect/builders.py
+++ b/src/py/mat3ra/made/tools/build/defect/builders.py
@@ -149,12 +149,12 @@ def create_material_with_additional_layers_int(self, material: Material, added_t
 
         new_material = material.clone()
         termination = Termination.from_string(new_material.metadata.get("build").get("termination"))
-        build_config = new_material.metadata.get("build").get("configuration").copy()
+        build_config = new_material.metadata.get("build").get("configuration")
 
         if build_config["type"] != "SlabConfiguration":
             raise ValueError("Material is not a slab.")
         build_config.pop("type")
-        build_config["thickness"] += added_thickness
+        build_config["thickness"] = build_config["thickness"] + added_thickness
 
         new_slab_config = SlabConfiguration(**build_config)
         material_with_additional_layers = create_slab(new_slab_config, termination)