SQLAlchemy update record with case clause and enum

I have defined the following model and enum:

class StatusEnum(enum.Enum):
    NEW = 'NEW'
    PROCESSED = 'PROCESSED'
    IN_PROGRESS = 'IN_PROGRESS'

class RequestLog(Base):
    __tablename__ = 'request_log'

    ...
    status = Column(Enum(StatusEnum))
    ...

I'm trying to update the record in the following way:

>>> session.query(RequestLog).filter(RequestLog.id.in_([8])).update(
{'status': case(
    [(RequestLog.attempt_done_count == RequestLog.attempt_count - 1, StatusEnum.PROCESSED)],
    else_=StatusEnum.IN_PROGRESS)},
synchronize_session=False)

During this, I received an error:

sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) can't adapt type 'StatusEnum' [SQL: 'UPDATE request_log SET status=CASE WHEN (request_log.attempt_done_count = request_log.attempt_count - %(attempt_count_1)s) THEN %(param_1)s ELSE %(param_2)s END WHERE request_log.id IN (%(id_1)s)'] [parameters: {'param_2': <StatusEnum.IN_PROGRESS: 'IN_PROGRESS'>, 'attempt_count_1': 1, 'param_1': <StatusEnum.PROCESSED: 'PROCESSED'>, 'id_1': 8}]