Species of Corynebacterium are Gram-positive bacilli, often considered contaminants, but some non-diphtheritic species are now recognized as opportunistic pathogens. We report a case of infective endocarditis caused by Corynebacterium argentoratense, an extremely rare species, in a 59-year-old patient with a history of severe pneumonia. This case highlights the potential emergence of this species in severe human infections and the importance of cautious interpretation of positive blood cultures involving corynebacteria.