The Supreme Court has made it harder for a parent in a custody dispute to seek the immediate return of a child under an international treaty to deter child abduction.

The justices ruled unanimously Wednesday that a one-year clock begins ticking when a child is taken out of its country of residence, even if the parent left behind cannot determine where the child is living. In the one-year period, the Hague Convention on child abduction gives judges little option but to return the child to its home country.

After a year, judges have more discretion and must take account of evidence that the child is settled in its new home.

At issue is not the ultimate custody of the child, but in which nation’s courts the case will be heard.