diff --git a/stdlib/bytes.ml b/stdlib/bytes.ml
index b3e7679a6..193c3ceea 100644
--- a/stdlib/bytes.ml
+++ b/stdlib/bytes.ml
@@ -203,9 +203,6 @@ let mapi f s =
     r
   end
 
-let uppercase s = map Char.uppercase s
-let lowercase s = map Char.lowercase s
-
 let uppercase_ascii s = map Char.uppercase_ascii s
 let lowercase_ascii s = map Char.lowercase_ascii s
 
@@ -216,9 +213,6 @@ let apply1 f s =
     r
   end
 
-let capitalize s = apply1 Char.uppercase s
-let uncapitalize s = apply1 Char.lowercase s
-
 let capitalize_ascii s = apply1 Char.uppercase_ascii s
 let uncapitalize_ascii s = apply1 Char.lowercase_ascii s
 
@@ -267,3 +261,11 @@ type t = bytes
 
 let compare (x: t) (y: t) = Pervasives.compare x y
 external equal : t -> t -> bool = "caml_string_equal"
+
+(* Deprecated functions implemented via other deprecated functions *)
+[@@@ocaml.warning "-3"]
+let uppercase s = map Char.uppercase s
+let lowercase s = map Char.lowercase s
+
+let capitalize s = apply1 Char.uppercase s
+let uncapitalize s = apply1 Char.lowercase s
diff --git a/stdlib/bytes.mli b/stdlib/bytes.mli
index e4ceb0811..6cb4b1374 100644
--- a/stdlib/bytes.mli
+++ b/stdlib/bytes.mli
@@ -229,22 +229,46 @@ val rcontains_from : bytes -> int -> char -> bool
     position in [s]. *)
 
 val uppercase : bytes -> bytes
+  [@@ocaml.deprecated "Use Bytes.uppercase_ascii instead."]
 (** Return a copy of the argument, with all lowercase letters
-    translated to uppercase, including accented letters of the ISO
-    Latin-1 (8859-1) character set. *)
+   translated to uppercase, including accented letters of the ISO
+   Latin-1 (8859-1) character set.
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val lowercase : bytes -> bytes
+  [@@ocaml.deprecated "Use Bytes.lowercase_ascii instead."]
 (** Return a copy of the argument, with all uppercase letters
-    translated to lowercase, including accented letters of the ISO
-    Latin-1 (8859-1) character set. *)
+   translated to lowercase, including accented letters of the ISO
+   Latin-1 (8859-1) character set.
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val capitalize : bytes -> bytes
-(** Return a copy of the argument, with the first byte set to
-    uppercase. *)
+  [@@ocaml.deprecated "Use Bytes.capitalize_ascii instead."]
+(** Return a copy of the argument, with the first character set to uppercase,
+   using the ISO Latin-1 (8859-1) character set..
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val uncapitalize : bytes -> bytes
-(** Return a copy of the argument, with the first byte set to
-    lowercase. *)
+  [@@ocaml.deprecated "Use Bytes.uncapitalize_ascii instead."]
+(** Return a copy of the argument, with the first character set to lowercase,
+   using the ISO Latin-1 (8859-1) character set..
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
+
+val uppercase_ascii : bytes -> bytes
+(** Return a copy of the argument, with all lowercase letters
+   translated to uppercase, using the US-ASCII character set. *)
+
+val lowercase_ascii : bytes -> bytes
+(** Return a copy of the argument, with all uppercase letters
+   translated to lowercase, using the US-ASCII character set. *)
+
+val capitalize_ascii : bytes -> bytes
+(** Return a copy of the argument, with the first character set to uppercase,
+   using the US-ASCII character set. *)
+
+val uncapitalize_ascii : bytes -> bytes
+(** Return a copy of the argument, with the first character set to lowercase,
+   using the US-ASCII character set. *)
 
 type t = bytes
 (** An alias for the type of byte sequences. *)
@@ -390,11 +414,6 @@ let s = Bytes.of_string "hello"
 
 (**/**)
 
-val lowercase_ascii : bytes -> bytes
-val uppercase_ascii : bytes -> bytes
-val capitalize_ascii : bytes -> bytes
-val uncapitalize_ascii : bytes -> bytes
-
 (* The following is for system use only. Do not call directly. *)
 
 external unsafe_get : bytes -> int -> char = "%string_unsafe_get"
diff --git a/stdlib/char.mli b/stdlib/char.mli
index 88094bd2b..f70ab5ea5 100644
--- a/stdlib/char.mli
+++ b/stdlib/char.mli
@@ -27,10 +27,24 @@ val escaped : char -> string
    of OCaml. *)
 
 val lowercase : char -> char
-(** Convert the given character to its equivalent lowercase character. *)
+  [@@ocaml.deprecated "Use Char.lowercase_ascii instead."]
+(** Convert the given character to its equivalent lowercase character,
+   using the ISO Latin-1 (8859-1) character set.
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val uppercase : char -> char
-(** Convert the given character to its equivalent uppercase character. *)
+  [@@ocaml.deprecated "Use Char.uppercase_ascii instead."]
+(** Convert the given character to its equivalent uppercase character,
+   using the ISO Latin-1 (8859-1) character set.
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
+
+val lowercase_ascii : char -> char
+(** Convert the given character to its equivalent lowercase character,
+   using the US-ASCII character set. *)
+
+val uppercase_ascii : char -> char
+(** Convert the given character to its equivalent uppercase character,
+   using the US-ASCII character set. *)
 
 type t = char
 (** An alias for the type of characters. *)
@@ -47,9 +61,6 @@ val equal: t -> t -> bool
 
 (**/**)
 
-val lowercase_ascii : char -> char
-val uppercase_ascii : char -> char
-
 (* The following is for system use only. Do not call directly. *)
 
 external unsafe_chr : int -> char = "%identity"
diff --git a/stdlib/string.ml b/stdlib/string.ml
index f78e1395e..0cea7acb7 100644
--- a/stdlib/string.ml
+++ b/stdlib/string.ml
@@ -112,14 +112,6 @@ let contains_from s i c =
   B.contains_from (bos s) i c
 let rcontains_from s i c =
   B.rcontains_from (bos s) i c
-let uppercase s =
-  B.uppercase (bos s) |> bts
-let lowercase s =
-  B.lowercase (bos s) |> bts
-let capitalize s =
-  B.capitalize (bos s) |> bts
-let uncapitalize s =
-  B.uncapitalize (bos s) |> bts
 
 let uppercase_ascii s =
   B.uppercase_ascii (bos s) |> bts
@@ -134,3 +126,14 @@ type t = string
 
 let compare (x: t) (y: t) = Pervasives.compare x y
 external equal : string -> string -> bool = "caml_string_equal"
+
+(* Deprecated functions implemented via other deprecated functions *)
+[@@@ocaml.warning "-3"]
+let uppercase s =
+  B.uppercase (bos s) |> bts
+let lowercase s =
+  B.lowercase (bos s) |> bts
+let capitalize s =
+  B.capitalize (bos s) |> bts
+let uncapitalize s =
+  B.uncapitalize (bos s) |> bts
diff --git a/stdlib/string.mli b/stdlib/string.mli
index 1f6191512..3a0af298f 100644
--- a/stdlib/string.mli
+++ b/stdlib/string.mli
@@ -215,20 +215,46 @@ val rcontains_from : string -> int -> char -> bool
    position in [s]. *)
 
 val uppercase : string -> string
+  [@@ocaml.deprecated "Use String.uppercase_ascii instead."]
 (** Return a copy of the argument, with all lowercase letters
    translated to uppercase, including accented letters of the ISO
-   Latin-1 (8859-1) character set. *)
+   Latin-1 (8859-1) character set.
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val lowercase : string -> string
+  [@@ocaml.deprecated "Use String.lowercase_ascii instead."]
 (** Return a copy of the argument, with all uppercase letters
    translated to lowercase, including accented letters of the ISO
-   Latin-1 (8859-1) character set. *)
+   Latin-1 (8859-1) character set.
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val capitalize : string -> string
-(** Return a copy of the argument, with the first character set to uppercase. *)
+  [@@ocaml.deprecated "Use String.capitalize_ascii instead."]
+(** Return a copy of the argument, with the first character set to uppercase,
+   using the ISO Latin-1 (8859-1) character set..
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
 
 val uncapitalize : string -> string
-(** Return a copy of the argument, with the first character set to lowercase. *)
+  [@@ocaml.deprecated "Use String.uncapitalize_ascii instead."]
+(** Return a copy of the argument, with the first character set to lowercase,
+   using the ISO Latin-1 (8859-1) character set..
+   @deprecated Functions operating on Latin-1 character set are deprecated. *)
+
+val uppercase_ascii : string -> string
+(** Return a copy of the argument, with all lowercase letters
+   translated to uppercase, using the US-ASCII character set. *)
+
+val lowercase_ascii : string -> string
+(** Return a copy of the argument, with all uppercase letters
+   translated to lowercase, using the US-ASCII character set. *)
+
+val capitalize_ascii : string -> string
+(** Return a copy of the argument, with the first character set to uppercase,
+   using the US-ASCII character set. *)
+
+val uncapitalize_ascii : string -> string
+(** Return a copy of the argument, with the first character set to lowercase,
+   using the US-ASCII character set. *)
 
 type t = string
 (** An alias for the type of strings. *)
@@ -245,11 +271,6 @@ val equal: t -> t -> bool
 
 (**/**)
 
-val lowercase_ascii : string -> string
-val uppercase_ascii : string -> string
-val capitalize_ascii : string -> string
-val uncapitalize_ascii : string -> string
-
 (* The following is for system use only. Do not call directly. *)
 
 external unsafe_get : string -> int -> char = "%string_unsafe_get"