diff --git a/src/core/CCArray.ml b/src/core/CCArray.ml
index 2c338642..9ac0d744 100644
--- a/src/core/CCArray.ml
+++ b/src/core/CCArray.ml
@@ -44,6 +44,7 @@ let get_safe a i =
     None
 
 let map_inplace f a = Array.iteri (fun i e -> Array.unsafe_set a i (f e)) a
+let mapi_inplace f a = Array.iteri (fun i e -> Array.unsafe_set a i (f i e)) a
 let fold = Array.fold_left
 
 let foldi f acc a =
diff --git a/src/core/CCArray.mli b/src/core/CCArray.mli
index de08d819..a3258097 100644
--- a/src/core/CCArray.mli
+++ b/src/core/CCArray.mli
@@ -64,6 +64,10 @@ val map_inplace : ('a -> 'a) -> 'a t -> unit
 (** [map_inplace f a] replace all elements of [a] by its image by [f].
     @since 3.8 *)
 
+val mapi_inplace : (int -> 'a -> 'a) -> 'a t -> unit
+(** [mapi_inplace f a] replace all elements of [a] by its image by [f].
+    @since NEXT_RELEASE *)
+
 val fold : ('a -> 'b -> 'a) -> 'a -> 'b t -> 'a
 (** [fold f init a] computes [f (… (f (f init a.(0)) a.(1)) …) a.(n-1)],
     where [n] is the length of the array [a].
diff --git a/src/core/CCArrayLabels.mli b/src/core/CCArrayLabels.mli
index e9b2c649..2cddc210 100644
--- a/src/core/CCArrayLabels.mli
+++ b/src/core/CCArrayLabels.mli
@@ -62,6 +62,10 @@ val map_inplace : f:('a -> 'a) -> 'a t -> unit
 (** [map_inplace ~f a] replace all elements of [a] by its image by [f].
     @since 3.8 *)
 
+val mapi_inplace : f:(int -> 'a -> 'a) -> 'a t -> unit
+(** [mapi_inplace ~f a] replace all elements of [a] by its image by [f].
+    @since NEXT_RELEASE *)
+
 val fold : f:('a -> 'b -> 'a) -> init:'a -> 'b t -> 'a
 (** [fold ~f ~init a] computes [f (… (f (f init a.(0)) a.(1)) …) a.(n-1)],
     where [n] is the length of the array [a].