Indeed. I was surprised on one occasion when I had a block data subprogram in a file by itself, and did not link the corresponding OBJ file with the rest of the OBJ files from the other source files (error in makefile). Later, I learned a trick (Les Hatton was mentioned as the creator) to avoid this error: give a name to the block data, say, “BLOCK DATA BLK”, and add “EXTERNAL BLK” in the main program. With this change, a linker error will occur if the block data OBJ file is not included.