What is ironic about the narrator’s conversation with fortunato once they enter the catacombs?

Fortunado has a cough and a cold when they entered the catacombs. He insisted that he will not die from this and did not take it seriously. But then he did die in the end. It becomes ironic when he drink wine and thought of his cough with concern. It has been said that the author made the story like this because he is having a hard time of what will the conversation flow be between Fortunado, Montresor and Amontillado.