CBO choosing wrong index

For the following query, CBO chooses an index intersection plan of the indexes on S.u64 and S.u256. S.u64 is a column with 1..64 unique values, so the predicate S.u64 < 100 is not a good predicate to use the S.u64 index. The plan should only use the index on S.u256

select * from S where int64_default_null(S.u64) < 100 and int64_default_null(S.u256) = 10;