diff --git a/theories/lang/arc_cmra.v b/theories/lang/arc_cmra.v
index 596986c85a15be577355d4376e7c8094a934efb8..49478dc2434de287c8961bcbfcf3167cb0993f03 100644
--- a/theories/lang/arc_cmra.v
+++ b/theories/lang/arc_cmra.v
@@ -93,6 +93,7 @@ Definition Z_of_arcstrong_st (st : strong_stUR) : Z :=
   | Some (_, n) =>  Zpos n
   end.
 
+Local Open Scope Z_scope.
 
 Lemma strong_stUR_value st: 0 ≤ Z_of_arcstrong_st st.
 Proof. destruct st as [[]|]; simpl; lia. Qed.