diff --git a/src/core/CCResult.mli b/src/core/CCResult.mli
index a5b47bb6..04a69a5c 100644
--- a/src/core/CCResult.mli
+++ b/src/core/CCResult.mli
@@ -188,6 +188,9 @@ end
 (** {2 Collections} *)
 
 val map_l : ('a -> ('b, 'err) t) -> 'a list -> ('b list, 'err) t
+(** [map_l f l] apply [f] on every element of [l], and, in case of success for every
+    element, return [Ok (List.map f l)]. Otherwise, it fails, and the first error is
+    return.*)
 
 val fold_l : ('b -> 'a -> ('b, 'err) t) -> 'b -> 'a list -> ('b, 'err) t