The article describes the relationship between the interwar Czechoslovakia and the Holy See in the light of the materials of the Congregation for extraordinary ecclesiastical affairs (Segreteria di Stato, Sezione per i Rapporti con gli Stati, Archivio Storico, Congregazione degli Affari Ecclesiastici Straordinari, fondo Rapporti-Sessioni). These materials are compared with the sources from the Czech Archives, above all from the Ministry of Foreign Affaires. They show that the diplomatic conflict that broke out in 1925 was on the brink of exploding since 1921. The Holy See perceived the legalisation of Jan Hus Day in 1925 as a key issue, whilst the Czechoslovak political leadership, especially Edvard Beneš, underestimated the situation. The Czechoslovak leadership had to find a compromise not only with Vatican diplomacy, but also with the left-leaning public opinion in Czechoslovakia. Disinformation, or shifting information was also part of the difficult negotiation on mutual compromise.