diff --git a/src/core/CCString.cppo.ml b/src/core/CCString.cppo.ml
index 6a06e672..c41f04c0 100644
--- a/src/core/CCString.cppo.ml
+++ b/src/core/CCString.cppo.ml
@@ -306,13 +306,11 @@ let iter = String.iter
 #if OCAML_MAJOR >= 4
 
 let map = String.map
-let mapi = String.mapi
 let iteri = String.iteri
 
 #else
 
 let map f s = init (length s) (fun i -> f s.[i])
-let mapi f s = init (length s) (fun i -> f i s.[i])
 
 let iteri f s =
   for i = 0 to String.length s - 1 do
@@ -321,6 +319,16 @@ let iteri f s =
 
 #endif
 
+#if OCAML_MAJOR >= 4 && OCAML_MINOR >= 2
+
+let mapi = String.mapi
+
+#else
+
+let mapi f s = init (length s) (fun i -> f i s.[i])
+
+#endif
+
 let flat_map ?sep f s =
   let buf = Buffer.create (String.length s) in
   iteri