diff --git a/python/pydantic_core/core_schema.py b/python/pydantic_core/core_schema.py
index d03dded87..957ec85da 100644
--- a/python/pydantic_core/core_schema.py
+++ b/python/pydantic_core/core_schema.py
@@ -145,7 +145,7 @@ def context(self) -> ContextT:
         ...
 
     @property
-    def mode(self) -> Literal['python', 'json']:
+    def mode(self) -> Literal['python', 'json'] | str:
         """The serialization mode set during serialization."""
         ...