diff --git a/CHANGELOG.md b/CHANGELOG.md
index 277da4886f4cc651699c3df4ac0ec45b1ac4d221..f4532cf3fd9f7d93844f00bb499e2b965cf40757 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,7 +14,9 @@ API-breaking change is listed.
 - Add type class `TopSet` for sets with a `⊤` element. Provide instances for
   `boolset`, `propset`, and `coPset`.
 - Add `set_solver` support for `dom`.
-
+- Rename `vec_to_list_of_list` into `vec_to_list_to_vec`, and add new lemma
+  `list_to_vec_to_list` for the converse.
+- Add `Countable` instance for `vec`.
 
 ## std++ 1.2.1 (released 2019-08-29)
 
diff --git a/theories/vector.v b/theories/vector.v
index 027d9e7b2cd5ec11470bc5bdac38965703c171da..908eadce8b157a24a5bfe522d904886d2aab2328 100644
--- a/theories/vector.v
+++ b/theories/vector.v
@@ -4,6 +4,7 @@
 (lists of fixed length). It uses the definitions from the standard library, but
 renames or changes their notations, so that it becomes more consistent with the
 naming conventions in this development. *)
+From stdpp Require Import countable.
 From stdpp Require Export fin list.
 Set Default Proof Using "Type".
 Open Scope vector_scope.
@@ -123,7 +124,7 @@ Proof. done. Qed.
 Lemma vec_to_list_app {A n m} (v : vec A n) (w : vec A m) :
   vec_to_list (v +++ w) = vec_to_list v ++ vec_to_list w.
 Proof. by induction v; f_equal/=. Qed.
-Lemma vec_to_list_of_list {A} (l : list A): vec_to_list (list_to_vec l) = l.
+Lemma vec_to_list_to_vec {A} (l : list A): vec_to_list (list_to_vec l) = l.
 Proof. by induction l; f_equal/=. Qed.
 Lemma vec_to_list_length {A n} (v : vec A n) : length (vec_to_list v) = n.
 Proof. induction v; simpl; by f_equal. Qed.
@@ -142,6 +143,13 @@ Proof.
   revert w. induction v; intros w; inv_vec w; intros;
     simplify_eq/=; f_equal; eauto.
 Qed.
+Lemma list_to_vec_to_list {A n} (v : vec A n) :
+  list_to_vec (vec_to_list v) = eq_rect _ _ v _ (eq_sym (vec_to_list_length v)).
+Proof.
+  apply vec_to_list_inj2. rewrite vec_to_list_to_vec.
+  by destruct (eq_sym (vec_to_list_length v)).
+Qed.
+
 Lemma vlookup_middle {A n m} (v : vec A n) (w : vec A m) x :
   ∃ i : fin (n + S m), x = (v +++ x ::: w) !!! i.
 Proof.
@@ -153,11 +161,11 @@ Lemma vec_to_list_lookup_middle {A n} (v : vec A n) (l k : list A) x :
     ∃ i : fin n, l = take i v ∧ x = v !!! i ∧ k = drop (S i) v.
 Proof.
   intros H.
-  rewrite <-(vec_to_list_of_list l), <-(vec_to_list_of_list k) in H.
+  rewrite <-(vec_to_list_to_vec l), <-(vec_to_list_to_vec k) in H.
   rewrite <-vec_to_list_cons, <-vec_to_list_app in H.
   pose proof (vec_to_list_inj1 _ _ H); subst.
   apply vec_to_list_inj2 in H; subst. induction l. simpl.
-  - eexists 0%fin. simpl. by rewrite vec_to_list_of_list.
+  - eexists 0%fin. simpl. by rewrite vec_to_list_to_vec.
   - destruct IHl as [i ?]. exists (FS i). simpl. intuition congruence.
 Qed.
 Lemma vec_to_list_drop_lookup {A n} (v : vec A n) (i : fin n) :
@@ -306,7 +314,17 @@ Lemma vmap_replicate {A B} (f : A → B) n (x : A) :
   vmap f (vreplicate n x) = vreplicate n (f x).
 Proof. induction n; f_equal/=; auto. Qed.
 
-(* Vectors can be inhabited. *)
+(** Vectors are inhabited and countable *)
 Global Instance vec_0_inhabited T : Inhabited (vec T 0) := populate [#].
 Global Instance vec_inhabited `{Inhabited T} n : Inhabited (vec T n) :=
   populate (vreplicate n inhabitant).
+
+Instance vec_countable `{Countable A} n : Countable (vec A n).
+Proof.
+  apply (inj_countable vec_to_list (λ l,
+    guard (n = length l) as H; Some (eq_rect _ _ (list_to_vec l) _ (eq_sym H)))).
+  intros v. case_option_guard as Hn.
+  - rewrite list_to_vec_to_list.
+    rewrite (proof_irrel (eq_sym _) Hn). by destruct Hn.
+  - by rewrite vec_to_list_length in Hn.
+Qed.