diff --git a/bin/day2405.ml b/bin/day2405.ml
index d277594..103d8ef 100644
--- a/bin/day2405.ml
+++ b/bin/day2405.ml
@@ -39,13 +39,12 @@ let rec is_page_order_valid m pages =
     encountering an empty line.  Returns a pair [(rule_map, tail)]. 
     [tail] starts the line after the empty line. *)
 let parse_rules =
-  let re = Str.regexp_string "|" in
   let m = Hashtbl.create 17 in
   let rec impl = function
     | "" :: t -> (m, t)
     | [] -> failwith "parse_rules.impl"
     | h :: t -> (
-        match List.map int_of_string (Str.split re h) with
+        match Aoc.ints_of_string ~sep:"|" h with
         | [ a; b ] ->
             add_rule a b m;
             impl t
@@ -55,10 +54,9 @@ let parse_rules =
 
 (** [parse_page_orders lst] parses a list of page orders.  *)
 let parse_page_orders =
-  let re = Str.regexp_string "," in
   let rec impl acc = function
     | [] -> acc
-    | h :: t -> impl (List.map int_of_string (Str.split re h) :: acc) t
+    | h :: t -> impl (Aoc.ints_of_string ~sep:"," h :: acc) t
   in
   impl []
 
diff --git a/lib/aoc.ml b/lib/aoc.ml
index 1e87e34..1c0dbb0 100644
--- a/lib/aoc.ml
+++ b/lib/aoc.ml
@@ -1,4 +1,6 @@
-let ints_of_string s = List.map int_of_string (Str.split (Str.regexp " +") s)
+let ints_of_string ?(sep = " ") s =
+  List.map int_of_string (Str.split (Str.regexp sep) s)
+
 let distance1 a b = abs (a - b)
 
 let strings_of_file fname =
diff --git a/lib/aoc.mli b/lib/aoc.mli
index 04f2a41..473de53 100644
--- a/lib/aoc.mli
+++ b/lib/aoc.mli
@@ -1,6 +1,6 @@
-val ints_of_string : string -> int list
-(** [nums_from_string s] takes a string of space separated integers and gives
-    back a list of the integers. *)
+val ints_of_string : ?sep:string -> string -> int list
+(** [nums_from_string ?sep s] takes a string of integers separated by [sep] and
+    gives back a list of the integers.  By default [sep] is " " *)
 
 val distance1 : int -> int -> int
 (** [distance1 a b] returns the absolute difference between [a] and [b]. *)