diff --git a/src/map.ml b/src/map.ml
index 3c3ae0e..146055d 100644
--- a/src/map.ml
+++ b/src/map.ml
@@ -33,7 +33,7 @@ let set_view latlng ~zoom map =
   in
   ()
 
-let on : type kind. kind Event.sub -> (kind Event.t -> 'b) -> t -> unit =
+let on : type kind. kind Event.sub -> (kind Event.t -> unit) -> t -> unit =
  fun event handler map ->
   let name = Event.sub_to_string event in
   let handler v = handler @@ Event.of_jv event v in
diff --git a/src/map.mli b/src/map.mli
index b50e841..4b8db43 100644
--- a/src/map.mli
+++ b/src/map.mli
@@ -28,7 +28,7 @@ val get_container : t -> Brr.El.t
 
 (** [on event handler map] add an event listener on [map] for event [event] with
     handler [handler] *)
-val on : 'a Event.sub -> ('a Event.t -> 'b) -> t -> unit
+val on : 'a Event.sub -> ('a Event.t -> unit) -> t -> unit
 
 (** [get_center map] is the geographical center of the map view *)
 val get_center : t -> Latlng.t