--- calendar-2.04/configure.in~	2014-10-29 10:03:20.000000000 +0000
+++ calendar-2.04/configure.in	2024-05-31 17:39:52.981965618 +0100
@@ -56,6 +56,7 @@
   3.0*) echo "${ECHO_T}Unsupported version!"; exit 2;;
   3.*) OCAMLMAJOR=3; echo "${ECHO_T}Good!";;
   4.*) OCAMLMAJOR=4; echo "${ECHO_T}Good!";;
+  5.*) OCAMLMAJOR=5; echo "${ECHO_T}Good!";;
   *) echo "${ECHO_T}Unsupported version!"; exit 2;;
 esac
 
diff -ur calendar-2.04.old/src/date.ml calendar-2.04/src/date.ml
--- calendar-2.04.old/src/date.ml	2014-10-29 10:03:20.000000000 +0000
+++ calendar-2.04/src/date.ml	2024-05-31 18:02:28.444110805 +0100
@@ -70,7 +70,7 @@
 (* Constructors. *)
 
 let lt (d1 : int * int * int) (d2 : int * int * int) =
-  Pervasives.compare d1 d2 < 0
+  Stdlib.compare d1 d2 < 0
 
 (* [date_ok] returns [true] is the date belongs to the Julian period;
    [false] otherwise. *)
@@ -249,10 +249,10 @@
   let sub x y = { m = x.m - y.m; d = x.d - y.d }
   let opp x = { m = - x.m; d = - x.d }
 
-  (* exactly equivalent to [Pervasives.compare] but more flexible typing *)
+  (* exactly equivalent to [Stdlib.compare] but more flexible typing *)
   let compare x y =
-    let n = Pervasives.compare x.m y.m in
-    if n = 0 then Pervasives.compare x.d y.d else n
+    let n = Stdlib.compare x.m y.m in
+    if n = 0 then Stdlib.compare x.d y.d else n
   let equal x y = compare x y = 0
   let hash = Hashtbl.hash
 
diff -ur calendar-2.04.old/src/printer.ml calendar-2.04/src/printer.ml
--- calendar-2.04.old/src/printer.ml	2014-10-29 10:03:20.000000000 +0000
+++ calendar-2.04/src/printer.ml	2024-05-31 18:03:14.806779295 +0100
@@ -181,7 +181,7 @@
     let print_int pad k n = print_number fmt pad k (Lazy.force n) in
     let print_string pad s =
       let pad s = match pad with
-	| Uppercase -> String.uppercase s
+	| Uppercase -> String.uppercase_ascii s
 	| Empty | Zero | Blank -> s
       in
       Format.pp_print_string fmt (pad (Lazy.force s))
@@ -236,7 +236,7 @@
 	| 'n' -> print_char '\n'
 	| 'p' -> print_string pad apm
 	| 'P' ->
-	    Format.pp_print_string fmt (String.lowercase (Lazy.force apm))
+	    Format.pp_print_string fmt (String.lowercase_ascii (Lazy.force apm))
 	| 'r' ->
 	    print_time pad shour;
 	    print_char ' ';
diff -ur calendar-2.04.old/src/utils.ml calendar-2.04/src/utils.ml
--- calendar-2.04.old/src/utils.ml	2014-10-29 10:03:20.000000000 +0000
+++ calendar-2.04/src/utils.ml	2024-05-31 18:02:28.445110798 +0100
@@ -29,8 +29,8 @@
 
 module Int = struct
   type t = int
-  let equal = Pervasives.(=)
-  let compare = Pervasives.compare
+  let equal = Stdlib.(=)
+  let compare = Stdlib.compare
   let hash = Hashtbl.hash
 end