diff --git a/theories/pttdom.v b/theories/pttdom.v
index 7739e8c..315fa6d 100644
--- a/theories/pttdom.v
+++ b/theories/pttdom.v
@@ -205,6 +205,7 @@ Section derived.
  Lemma eqv11 x y z: eqv' x y -> eqv' y z -> x ≡ z.
  Proof. move=> /= -> ->. apply cnvI. Qed.
 
+ #[non_forgetful_inheritance]
  HB.instance Definition pttdom_elabel := 
    Elabel_of_Setoid.Build X eqv'_sym eqv01 eqv11.