diff --git a/core/CCHeap.ml b/core/CCHeap.ml
index 698ca2cf..25f9d6f5 100644
--- a/core/CCHeap.ml
+++ b/core/CCHeap.ml
@@ -99,7 +99,7 @@ module type S = sig
   val of_gen : t -> elt gen -> t
   val to_gen : t -> elt gen
 
-  val to_tree : t -> elt tree
+  val to_tree : t -> elt ktree
 end
 
 module Make(E : PARTIAL_ORD) = struct
diff --git a/core/CCHeap.mli b/core/CCHeap.mli
index e265aef4..169b12fd 100644
--- a/core/CCHeap.mli
+++ b/core/CCHeap.mli
@@ -99,7 +99,7 @@ module type S = sig
   val of_gen : t -> elt gen -> t
   val to_gen : t -> elt gen
 
-  val to_tree : t -> elt tree
+  val to_tree : t -> elt ktree
 end
 
 module Make(E : PARTIAL_ORD) : S with type elt = E.t