Among the extensive preserved collection of documentation on Malbork’s economy are also contracts made between monarchs and subsequent economists. One such document, containing a contract for the years 1651–1653 between King John Casimir and the starost of Sztum Zygmunt Guldenstern, was recently published in the “Komunikaty Mazursko-Warmińskie”. In this study, the author conducted a detailed analysis of the text of this contract, listing all the obligations of the counterparty in turn. Then, primarily based on the treasury receipt preserved in the Crown Treasury Archive, as well as other sources, an attempt was made to show whether, to what extent, and in what scope, Zygmunt Guldenstern fulfilled the obligations imposed on him in the lease agreement.