diff --git a/src/threads/CCLock.ml b/src/threads/CCLock.ml
index 915a8d25..3a635482 100644
--- a/src/threads/CCLock.ml
+++ b/src/threads/CCLock.ml
@@ -66,7 +66,7 @@ module LockRef = struct
   let update t f = t.content <- f t.content
 end
 
-let with_lock_as_ref l f =
+let with_lock_as_ref l ~f =
   Mutex.lock l.mutex;
   try
     let x = f l in
@@ -80,7 +80,7 @@ let with_lock_as_ref l f =
   let l = create 0 in
   let test_it l =
     with_lock_as_ref l
-      (fun r ->
+      ~f:(fun r ->
         let x = LockRef.get r in
         LockRef.set r (x+10);
         Thread.yield ();
diff --git a/src/threads/CCLock.mli b/src/threads/CCLock.mli
index 50a40fd7..c541e8ac 100644
--- a/src/threads/CCLock.mli
+++ b/src/threads/CCLock.mli
@@ -52,7 +52,7 @@ module LockRef : sig
   val update : 'a t -> ('a -> 'a) -> unit
 end
 
-val with_lock_as_ref : 'a t -> ('a LockRef.t -> 'b) -> 'b
+val with_lock_as_ref : 'a t -> f:('a LockRef.t -> 'b) -> 'b
 (** [with_lock_as_ref l f] calls [f] with a reference-like object
     that allows to manipulate the value of [l] safely.
     The object passed to [f] must not escape the function call