diff --git a/src/cloudevents/core/v1/exceptions.py b/src/cloudevents/core/v1/exceptions.py
index 7eacc9d..3b151fb 100644
--- a/src/cloudevents/core/v1/exceptions.py
+++ b/src/cloudevents/core/v1/exceptions.py
@@ -32,7 +32,8 @@ def __init__(self, errors: dict[str, list[BaseCloudEventException]]) -> None:
 
     def __str__(self) -> str:
         error_messages = [
-            f"{key}: {', '.join(str(e) for e in value)}" for key, value in self.errors.items()
+            f"{key}: {', '.join(str(e) for e in value)}"
+            for key, value in self.errors.items()
         ]
         return f"{super().__str__()}: {', '.join(error_messages)}"