diff --git a/theories/sets.v b/theories/sets.v
index 0402ebc74346de0ed3e4bc295ba9380adab62041..bb9c9ddd102c9267d4e632927f6a1bf63eb0aa69 100644
--- a/theories/sets.v
+++ b/theories/sets.v
@@ -20,7 +20,7 @@ Proof. by split; [split | |]; repeat intro. Qed.
 
 Lemma mkSet_elem_of {A} (f : A → Prop) x : (x ∈ mkSet f) = f x.
 Proof. done. Qed.
-Lemma mkSet_not_elem_of {A} (f : A → Prop) x : (x ∉ mkSet f) = (~f x).
+Lemma mkSet_not_elem_of {A} (f : A → Prop) x : (x ∉ mkSet f) = (¬f x).
 Proof. done. Qed.
 
 Instance set_ret : MRet set := λ A (x : A), {[ x ]}.