diff --git a/pydantic_ai_slim/pydantic_ai/models/__init__.py b/pydantic_ai_slim/pydantic_ai/models/__init__.py
index 79f603168..be88fe9bd 100644
--- a/pydantic_ai_slim/pydantic_ai/models/__init__.py
+++ b/pydantic_ai_slim/pydantic_ai/models/__init__.py
@@ -765,6 +765,9 @@ def _customize_tool_def(transformer: type[JsonSchemaTransformer], t: ToolDefinit
 
 
 def _customize_output_object(transformer: type[JsonSchemaTransformer], o: OutputObjectDefinition):
-    schema_transformer = transformer(o.json_schema, strict=True)
+    orig_schema = o.json_schema
+    schema_transformer = transformer(orig_schema, strict=True)
     son_schema = schema_transformer.walk()
-    return replace(o, json_schema=son_schema)
+    if son_schema is orig_schema:
+        return o
+    return type(o)(**{**o.__dict__, "json_schema": son_schema})