diff --git a/src/core/CCFun.cppo.ml b/src/core/CCFun.cppo.ml
index c14cdb84..b8927c81 100644
--- a/src/core/CCFun.cppo.ml
+++ b/src/core/CCFun.cppo.ml
@@ -15,6 +15,16 @@ let (@@) f x = f x
 
 #endif
 
+#if OCAML_MAJOR >= 4 && OCAML_MINOR >= 3
+
+let opaque_identity = Sys.opaque_identity
+
+#else
+
+let opaque_identity x = x
+
+#endif
+
 let compose f g x = g (f x)
 
 let compose_binop f g x y = g (f x) (f y)
diff --git a/src/core/CCFun.mli b/src/core/CCFun.mli
index 7d731708..6f8a1c0e 100644
--- a/src/core/CCFun.mli
+++ b/src/core/CCFun.mli
@@ -65,6 +65,12 @@ val finally2 : h:(unit -> _) -> ('a -> 'b -> 'c) -> 'a -> 'b -> 'c
     [h ()] is called whether [f x y] rose an exception or not.
     @since 0.16 *)
 
+val opaque_identity : 'a -> 'a
+(** [opaque_identity x] is like [x], but prevents Flambda from using [x]'s
+    definition for optimizing it (flambda is an optimization/inlining pass
+    in OCaml >= 4.03).
+    @since NEXT_RELEASE *)
+
 (** {2 Monad}
 
 Functions with a fixed domain are monads in their codomain *)
diff --git a/src/core/CCString.cppo.ml b/src/core/CCString.cppo.ml
index b476f92f..8a510d4e 100644
--- a/src/core/CCString.cppo.ml
+++ b/src/core/CCString.cppo.ml
@@ -639,6 +639,26 @@ let exists2 p s1 s2 =
   try iter2 (fun c1 c2 -> if p c1 c2 then raise MyExit) s1 s2; false
   with MyExit -> true
 
+(** {2 Ascii functions} *)
+
+#if OCAML_MAJOR >= 4 && OCAML_MINOR >= 3
+
+let capitalize_ascii = String.capitalize_ascii
+let uncapitalize_ascii = String.uncapitalize_ascii
+let uppercase_ascii = String.uppercase_ascii
+let lowercase_ascii = String.lowercase_ascii
+
+#else
+
+let capitalize_ascii = String.capitalize
+let uncapitalize_ascii = String.uncapitalize
+let uppercase_ascii = String.uppercase
+let lowercase_ascii = String.lowercase
+
+#endif
+
+
+
 let pp buf s =
   Buffer.add_char buf '"';
   Buffer.add_string buf s;
diff --git a/src/core/CCString.mli b/src/core/CCString.mli
index a61d52fd..edee2895 100644
--- a/src/core/CCString.mli
+++ b/src/core/CCString.mli
@@ -378,6 +378,24 @@ val exists2 : (char -> char -> bool) -> string -> string -> bool
     @raise Invalid_argument if the strings have not the same length
     @since 0.12 *)
 
+(** {2 Ascii functions}
+
+    Those functions are deprecated in {!String} since 4.03, so we provide
+    a stable alias for them even in older versions *)
+
+val capitalize_ascii : string -> string
+(** See {!String}. @since NEXT_RELEASE *)
+
+val uncapitalize_ascii : string -> string
+(** See {!String}. @since NEXT_RELEASE *)
+
+val uppercase_ascii : string -> string
+(** See {!String}. @since NEXT_RELEASE *)
+
+val lowercase_ascii : string -> string
+(** See {!String}. @since NEXT_RELEASE *)
+
+
 (** {2 Splitting} *)
 
 module Split : sig