diff --git a/src/core/CCHeap.ml b/src/core/CCHeap.ml
index 25f9d6f5..db84107a 100644
--- a/src/core/CCHeap.ml
+++ b/src/core/CCHeap.ml
@@ -102,7 +102,7 @@ module type S = sig
   val to_tree : t -> elt ktree
 end
 
-module Make(E : PARTIAL_ORD) = struct
+module Make(E : PARTIAL_ORD) : S with type elt = E.t = struct
   type elt = E.t
 
   type t =
diff --git a/src/core/CCVector.ml b/src/core/CCVector.ml
index e8f0d741..de490786 100644
--- a/src/core/CCVector.ml
+++ b/src/core/CCVector.ml
@@ -157,15 +157,15 @@ let append a b =
 *)
 
 let get v i =
-  if i < 0 || i >= v.size then failwith "Vector.get";
+  if i < 0 || i >= v.size then invalid_arg "Vector.get";
   Array.unsafe_get v.vec i
 
 let set v i x =
-  if i < 0 || i >= v.size then failwith "Vector.set";
+  if i < 0 || i >= v.size then invalid_arg "Vector.set";
   Array.unsafe_set v.vec i x
 
 let remove v i =
-  if i < 0 || i >= v.size then failwith "Vector.remove";
+  if i < 0 || i >= v.size then invalid_arg "Vector.remove";
   (* if v.(i) not the last element, then put last element at index i *)
   if i < v.size - 1
     then v.vec.(i) <- v.vec.(v.size - 1);
@@ -204,22 +204,23 @@ let compare cmp v1 v2 =
         if c = 0 then check (i+1) else c
   in check 0
 
+exception Empty
+
 let pop_exn v =
-  if v.size = 0
-    then failwith "Vector.pop on empty vector";
+  if v.size = 0 then raise Empty;
   v.size <- v.size - 1;
   let x = v.vec.(v.size) in
   x
 
 let pop v =
   try Some (pop_exn v)
-  with Failure _ -> None
+  with Empty -> None
 
 let top v =
   if v.size = 0 then None else Some v.vec.(v.size-1)
 
 let top_exn v =
-  if v.size = 0 then failwith "Vector.top";
+  if v.size = 0 then raise Empty;
   v.vec.(v.size-1)
 
 (*$T
diff --git a/src/core/CCVector.mli b/src/core/CCVector.mli
index e9362f75..79cc9798 100644
--- a/src/core/CCVector.mli
+++ b/src/core/CCVector.mli
@@ -92,12 +92,15 @@ val equal : 'a equal -> ('a,_) t equal
 val compare : 'a ord -> ('a,_) t ord
 (** Total ordering on vectors: Lexicographic comparison. *)
 
+exception Empty
+(** Raised on empty stack *)
+
 val pop : ('a, rw) t -> 'a option
 (** Remove last element, or [None] *)
 
 val pop_exn : ('a, rw) t -> 'a
 (** remove last element, or raise a Failure if empty
-    @raise Failure on an empty vector *)
+    @raise Empty on an empty vector *)
 
 val top : ('a, _) t -> 'a option
 (** Top element, if present
@@ -105,7 +108,7 @@ val top : ('a, _) t -> 'a option
 
 val top_exn : ('a, _) t -> 'a
 (** Top element, if present
-    @raise Failure on an empty vector
+    @raise Empty on an empty vector
     @since 0.6 *)
 
 val copy : ('a,_) t -> ('a,'mut) t
@@ -178,11 +181,11 @@ val (>|=) : ('a,_) t -> ('a -> 'b) -> ('b, 'mut) t
 
 val get : ('a,_) t -> int -> 'a
 (** access element by its index, or
-    @raise Failure if bad index *)
+    @raise Invalid_argument if bad index *)
 
 val set : ('a, rw) t -> int -> 'a -> unit
 (** modify element at given index, or
-    @raise Failure if bad index *)
+    @raise Invalid_argument if bad index *)
 
 val remove : ('a, rw) t -> int -> unit
 (** Remove the [n-th] element of the vector. Does {b NOT} preserve the order