diff --git a/Mathlib/Data/Set/Lattice.lean b/Mathlib/Data/Set/Lattice.lean
index 646e324cf57607..45ee06f4df75f3 100644
--- a/Mathlib/Data/Set/Lattice.lean
+++ b/Mathlib/Data/Set/Lattice.lean
@@ -239,7 +239,7 @@ theorem mem_iInter₂_of_mem {s : ∀ i, κ i → Set α} {a : α} (h : ∀ i j,
   mem_iInter₂.2 h
 #align set.mem_Inter₂_of_mem Set.mem_iInter₂_of_mem
 
-instance Set.completeAtomicBooleanAlgebra : CompleteAtomicBooleanAlgebra (Set α) :=
+instance completeAtomicBooleanAlgebra : CompleteAtomicBooleanAlgebra (Set α) :=
   { instBooleanAlgebraSet with
     le_sSup := fun s t t_in a a_in => ⟨t, t_in, a_in⟩
     sSup_le := fun s t h a ⟨t', ⟨t'_in, a_in⟩⟩ => h t' t'_in a_in