diff --git a/rfc/4/index.md b/rfc/4/index.md
index 08975c95..1512ed6f 100644
--- a/rfc/4/index.md
+++ b/rfc/4/index.md
@@ -262,6 +262,7 @@ In Pydantic:
 
 ```python
 from enum import Enum
+from typing import Literal
 from pydantic import BaseModel
 
 class AnatomicalOrientationValue(str, Enum):
@@ -316,7 +317,7 @@ class AnatomicalOrientation(Orientation):
     """
     Anatomical orientation specific implementation.
     """
-    type: str = "anatomical"
+    type: Literal["anatomical"]
     value: AnatomicalOrientationValue
 ```