diff --git a/src/cloudevents/core/v1/exceptions.py b/src/cloudevents/core/v1/exceptions.py
index 8f11517..ba6b63a 100644
--- a/src/cloudevents/core/v1/exceptions.py
+++ b/src/cloudevents/core/v1/exceptions.py
@@ -42,6 +42,7 @@ class MissingRequiredAttributeError(BaseCloudEventException, ValueError):
     """
 
     def __init__(self, attribute_name: str) -> None:
+        self.attribute_name: str = attribute_name
         super().__init__(f"Missing required attribute: '{attribute_name}'")