diff --git a/README.md b/README.md
index 3106b3e..90e2e46 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,7 @@ class Bar(BaseModel):
    banana: str = 'y'
 
 class Spam(BaseModel):
+   # PydanticObjectId is an alias to Annotated[ObjectId, ObjectIdAnnotation]
    id: Optional[PydanticObjectId] = None
    foo: Foo
    bars: List[Bar]
diff --git a/pydantic_mongo/__init__.py b/pydantic_mongo/__init__.py
index a098bb9..74e0bf9 100644
--- a/pydantic_mongo/__init__.py
+++ b/pydantic_mongo/__init__.py
@@ -1,5 +1,5 @@
 from .abstract_repository import AbstractRepository
-from .fields import ObjectIdField, PydanticObjectId
+from .fields import ObjectIdAnnotation, ObjectIdField, PydanticObjectId
 from .version import __version__  # noqa: F401
 
-__all__ = ["ObjectIdField", "PydanticObjectId", "AbstractRepository"]
+__all__ = ["AbstractRepository", "ObjectIdField", "ObjectIdAnnotation", "PydanticObjectId"]