diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+### 0.2.1
+
+* Add `ToString` instance for `case-insensitive`.
+
 #### 0.2.0.2
 
 * Allow `text 1.2.*`
diff --git a/src/Data/String/ToString.hs b/src/Data/String/ToString.hs
--- a/src/Data/String/ToString.hs
+++ b/src/Data/String/ToString.hs
@@ -2,10 +2,9 @@
     FlexibleInstances
   , TypeSynonymInstances
   #-}
-module Data.String.ToString
-  ( ToString (..)
-  ) where
+module Data.String.ToString (ToString (..)) where
 
+import Data.CaseInsensitive (CI, foldedCase)
 import qualified Data.ByteString.Lazy.UTF8 as LBU
 import qualified Data.ByteString.UTF8      as SBU
 import qualified Data.Text                 as ST
@@ -28,3 +27,6 @@
 
 instance ToString LT.Text where
   toString = LT.unpack
+
+instance ToString s => ToString (CI s) where
+  toString = toString . foldedCase
diff --git a/tostring.cabal b/tostring.cabal
--- a/tostring.cabal
+++ b/tostring.cabal
@@ -1,5 +1,5 @@
 name:                tostring
-version:             0.2.0.2
+version:             0.2.1
 synopsis:            The ToString class
 description:         A type class for converting text types to String.
 license:             BSD3
@@ -25,5 +25,6 @@
   exposed-modules:   Data.String.ToString
   build-depends:
       base == 4.*
+    , case-insensitive >= 1.0 && < 1.3
     , text >= 0.11 && < 1.3
     , utf8-string == 0.3.*