Throughout his life, Bok was deeply interested in astrology, as well as in the music of the Finnish composer Jean Sibelius, with whom Bok had a correspondence. (Bok's copy of Karl Ekman's "Jean Sibelius: His Life and Personality" 1938, for example, is annotated with Bok's comments and astrological charts.) As the years passed, Bok became prone to disagreements with editors over money and artistic issues; he grew reclusive and mystical, and preoccupied with the occult. He eked out a living, often in near poverty, until his death in 1964. He died, apparently of a heart attack (he "starved to death" according to Ackerman), at the age of 49. ISFDB catalogs only a few 1956 interior illustrations after March 1954, his last for "Weird Tales", and only two cover illustrations after January 1957.