diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for readline-in-other-words
 
+## 0.1.0.1 -- 2021-11-04
+
+* Add missing `Functor` instance on type used as functor for `Optional`.
+
 ## 0.1.0.0 -- 2021-11-04
 
 * First version. Released on an unsuspecting world.
diff --git a/readline-in-other-words.cabal b/readline-in-other-words.cabal
--- a/readline-in-other-words.cabal
+++ b/readline-in-other-words.cabal
@@ -1,7 +1,7 @@
 cabal-version:  2.4
 name:           readline-in-other-words
 synopsis:       Readline effect for in-other-words.
-category:       User Interfaces, Effect
+category:       User Interfaces, Effect, in-other-words, Command Line
 homepage:       https://github.com/lehmacdj/readline-in-other-words#readme
 bug-reports:    https://github.com/lehmacdj/readline-in-other-words/issues
 author:         Devin Lehmacher
@@ -22,7 +22,7 @@
 -- 1. changelog
 -- 2. make tag; update @source-repository this@ clause
 -- 3. right here
-version: 0.1.0.0
+version: 0.1.0.1
 
 source-repository head
   type: git
@@ -31,7 +31,7 @@
 source-repository this
   type: git
   location: git://github.com/lehmacdj/readline-in-other-words.git
-  tag: 0.1.0.0
+  tag: 0.1.0.1
 
 common options
   ghc-options: -Wall -fplugin=Control.Effect.Plugin
diff --git a/src/Control/Effect/Readline/Internal.hs b/src/Control/Effect/Readline/Internal.hs
--- a/src/Control/Effect/Readline/Internal.hs
+++ b/src/Control/Effect/Readline/Internal.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DerivingStrategies #-}
 {-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE FlexibleContexts #-}
@@ -126,6 +127,7 @@
 data HandleInterrupt :: Effect where
   WithInterrupt :: m a -> HandleInterrupt m a
   HandleInterrupt :: m a -> m a -> HandleInterrupt m a
+  deriving (Functor)
 
 -- | If Ctrl-C is pressed during the given action, enables interrupt handling
 -- within the nested scope. For example: