diff --git a/theories/list_numbers.v b/theories/list_numbers.v
index d41a94f81011864bfa2bb4fb12a0d59f075b990f..7ca1548f4056d004ca305df0f85f8005e03a3ec5 100644
--- a/theories/list_numbers.v
+++ b/theories/list_numbers.v
@@ -200,7 +200,7 @@ Section sum_list.
   Proof.
     induction l; simpl; rewrite ?reverse_cons, ?sum_list_with_app; simpl; lia.
   Qed.
-  Lemma sum_list_with_in x (f : A → nat) l : x ∈ l → f x ≤ sum_list_with f l.
+  Lemma sum_list_with_in x (f : A → nat) ls : x ∈ ls → f x ≤ sum_list_with f ls.
   Proof. induction 1; simpl; lia. Qed.
   Lemma join_reshape szs l :
     sum_list szs = length l → mjoin (reshape szs l) = l.