diff --git a/packages/js/js.ml b/packages/js/js.ml
index 5bd95d8dd..3ef96a561 100644
--- a/packages/js/js.ml
+++ b/packages/js/js.ml
@@ -3370,23 +3370,23 @@ let logMany = Console.logMany
 module Set = struct
   (** Provides bindings for ES6 Set *)
 
-  type t
+  type 'a t
 end
 
 module WeakSet = struct
   (** Provides bindings for ES6 WeakSet *)
 
-  type t
+  type 'a t
 end
 
 module Map = struct
   (** Provides bindings for ES6 Map *)
 
-  type t
+  type ('k, 'v) t
 end
 
 module WeakMap = struct
   (** Provides bindings for ES6 WeakMap *)
 
-  type t
+  type ('k, 'v) t
 end