A U.S. citizen has been denied entry into Poland after her passport was deemed defaced with handwritten notes, according to local border officials. The incident occurred at Krakow’s Balice airport shortly after midnight when the traveler arrived on a flight from London.

According to Justyna Drozdz, a spokeswoman for the local border security, the woman was stopped during passport control because her document displayed handwritten entries indicating various locations and airport names next to the visa stamps from countries she had visited.

The traveler explained to border security personnel that she was not aware that writing on passports or identification documents was prohibited. As a result, she has been informed that she must remain at the airport and will be booked on a return flight to London scheduled for Thursday.

Generally, it is against regulations for passport holders to write anything in their passports, aside from the necessary signature and emergency contact information. Airlines and immigration authorities tend to refuse boarding or entry if they determine that a passport has been damaged or altered in any way. It remains unclear why officials at other ports of entry had not raised concerns about the woman’s passport previously.