diff --git a/src/data/CCCache.ml b/src/data/CCCache.ml
index 3437d493..ec956458 100644
--- a/src/data/CCCache.ml
+++ b/src/data/CCCache.ml
@@ -30,6 +30,15 @@ type ('a, 'b) callback = in_cache:bool -> 'a -> 'b -> unit
 
 let clear c = c.clear ()
 
+let add c x y =
+  try
+    (* check that x is not bound (see invariants) *)
+    let _ = c.get x in
+    false
+  with Not_found ->
+    c.set x y;
+    true
+
 let default_callback_ ~in_cache:_ _ _ = ()
 
 let with_cache ?(cb=default_callback_) c f x =
diff --git a/src/data/CCCache.mli b/src/data/CCCache.mli
index 1caac2ed..e689f090 100644
--- a/src/data/CCCache.mli
+++ b/src/data/CCCache.mli
@@ -71,6 +71,11 @@ val size : (_,_) t -> int
 val iter : ('a,'b) t -> ('a -> 'b -> unit) -> unit
 (** Iterate on cached values. Should yield [size cache] pairs. *)
 
+val add : ('a, 'b) t -> 'a -> 'b -> bool
+(** Manually add a cached value. Returns [true] if the value has succesfully
+    been added, and [false] if the value was already bound.
+    @since NEXT_RELEASE *)
+
 val dummy : ('a,'b) t
 (** Dummy cache, never stores any value *)