The next time you try to bring antiques into the U.S., think again: if they look old enough and dont have any documentation, customs officials might just seize them as potentially looted cultural artifacts.

That was the case in 2009 when the Ancient Coin Collectors Guild, a non-profit group that seeks to ensure a free market for the exchange and sale of collector coins, bought 23 ancient coins of unknown provenance from a London dealer. U.S. Customs seized the coins, which ranged from 1,000 to 2,000 years old, due to the possibility that they were looted objects, according to the Blog of Legal Times.

A federal judge in Maryland dismissed on summary judgment the Guilds lawsuit against U.S. Customs and Border Protection last week, citing procedural issues but also ruling that it is better to err on the side of restricting imports when their origin is unclear.

Looted objects are, presumably, extremely unlikely to carry documentation, or at least accurate documentation, of when and where they were discovered and when they were exported from the country in which they were discovered, the judge wrote in her opinion.

Moreover, the judge found that the burden of proof rests with the importer of artifacts, who must demonstrate that they are legitimate; otherwise, the State Department can rightfully restrict their importation.