diff --git a/lib/aoc.ml b/lib/aoc.ml
index 05a23c4..a5b537e 100644
--- a/lib/aoc.ml
+++ b/lib/aoc.ml
@@ -10,7 +10,7 @@ let main prep parts =
     | [| _; fname |] ->
         let lines = prep fname in
         let do_part i (fmt, fn) =
-          Printf.printf "Part %d = %s\n" i (fmt (fn lines))
+          Printf.printf "Part %d = %s\n" (i + 1) (fmt (fn lines))
         in
         List.iteri do_part parts;
         exit 0