Failure to appoint a guardian ad litem (GAL) was harmless where the father’s mental illness prevented him from caring for the minor. The minor was removed from her mother due to sexual abuse and the mother’s substance abuse. At the time, appellant, the minor’s presumed father, was institutionalized under an LPS conservatorship based on his history of mental illness, and could not care for the minor. The father appeared in court through a court-appointed GAL. He was denied services under section 361.5, subdivision (e)(1) because he was institutionalized, and services would be detrimental to the minor. The minor was returned to the mother for a time, and then a new dependency proceeding was initiated when the mother relapsed. No GAL was appointed for the father and his previous GAL did not appear for him. Eventually parental rights were terminated. On appeal, the father contended that the juvenile court violated his due process rights by failing to appoint a GAL. The appellate court held that the juvenile court’s failure to comply with section 372 did not violate the father’s due process rights. The failure to appoint a GAL is not jurisdictional. If the person’s interests were not substantially prejudiced as a result, there is no reversible error. Here, the father’s interests were not substantially prejudiced, and the error was harmless. There was no doubt that father could not care for his daughter, and placement with him was out of the question. The appointment of a GAL would not have changed the outcome.