diff --git a/src/Init/Control/Option.lean b/src/Init/Control/Option.lean
index ebdcb40e97..4bf6f19c8b 100644
--- a/src/Init/Control/Option.lean
+++ b/src/Init/Control/Option.lean
@@ -10,7 +10,7 @@ import Init.Control.Except
 
 universe u v
 
-instance : ToBool (Option α) := ⟨Option.toBool⟩
+instance : ToBool (Option α) := ⟨Option.isSome⟩
 
 def OptionT (m : Type u → Type v) (α : Type u) : Type v :=
   m (Option α)
diff --git a/src/Init/Data/Option/Basic.lean b/src/Init/Data/Option/Basic.lean
index e6344f0320..bd0d091feb 100644
--- a/src/Init/Data/Option/Basic.lean
+++ b/src/Init/Data/Option/Basic.lean
@@ -21,15 +21,13 @@ def getM [Alternative m] : Option α → m α
 @[deprecated getM] def toMonad [Monad m] [Alternative m] : Option α → m α :=
   getM
 
-@[inline] def toBool : Option α → Bool
-  | some _ => true
-  | none   => false
-
 /-- Returns `true` on `some x` and `false` on `none`. -/
 @[inline] def isSome : Option α → Bool
   | some _ => true
   | none   => false
 
+@[deprecated isSome, inline] def toBool : Option α → Bool := isSome
+
 /-- Returns `true` on `none` and `false` on `some x`. -/
 @[inline] def isNone : Option α → Bool
   | some _ => false