diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 0.4.23
+
+* Case insensitive cookie domains [#158](https://github.com/snoyberg/http-client/issues/158)
+
 ## 0.4.22
 
 * ProxyConnectException now returns Right HttpException. [#155](https://github.com/snoyberg/http-client/pull/155)
diff --git a/Network/HTTP/Client/Cookies.hs b/Network/HTTP/Client/Cookies.hs
--- a/Network/HTTP/Client/Cookies.hs
+++ b/Network/HTTP/Client/Cookies.hs
@@ -52,13 +52,17 @@
 
 -- | This corresponds to the subcomponent algorithm entitled \"Domain Matching\" detailed
 -- in section 5.1.3
-domainMatches :: BS.ByteString -> BS.ByteString -> Bool
-domainMatches string domainString
+domainMatches :: BS.ByteString -- ^ Domain to test
+              -> BS.ByteString -- ^ Domain from a cookie
+              -> Bool
+domainMatches string' domainString'
   | string == domainString = True
   | BS.length string < BS.length domainString + 1 = False
   | domainString `BS.isSuffixOf` string && BS.singleton (BS.last difference) == "." && not (isIpAddress string) = True
   | otherwise = False
   where difference = BS.take (BS.length string - BS.length domainString) string
+        string = CI.foldCase string'
+        domainString = CI.foldCase domainString'
 
 -- | This corresponds to the subcomponent algorithm entitled \"Paths\" detailed
 -- in section 5.1.4
@@ -136,7 +140,7 @@
 computeCookieString request cookie_jar now is_http_api = (output_line, cookie_jar')
   where matching_cookie cookie = condition1 && condition2 && condition3 && condition4
           where condition1
-                  | cookie_host_only cookie = Req.host request == cookie_domain cookie
+                  | cookie_host_only cookie = CI.foldCase (Req.host request) == CI.foldCase (cookie_domain cookie)
                   | otherwise = domainMatches (Req.host request) (cookie_domain cookie)
                 condition2 = pathMatches (Req.path request) (cookie_path cookie)
                 condition3
diff --git a/Network/HTTP/Client/Types.hs b/Network/HTTP/Client/Types.hs
--- a/Network/HTTP/Client/Types.hs
+++ b/Network/HTTP/Client/Types.hs
@@ -55,6 +55,7 @@
 import Data.Text (Text)
 import Data.Streaming.Zlib (ZlibException)
 import Control.Concurrent.MVar (MVar)
+import Data.CaseInsensitive as CI
 
 -- | An @IO@ action that represents an incoming response body coming from the
 -- server. Data provided by this action has already been gunzipped and
@@ -159,7 +160,7 @@
 instance Eq Cookie where
   (==) a b = name_matches && domain_matches && path_matches
     where name_matches = cookie_name a == cookie_name b
-          domain_matches = cookie_domain a == cookie_domain b
+          domain_matches = CI.foldCase (cookie_domain a) == CI.foldCase (cookie_domain b)
           path_matches = cookie_path a == cookie_path b
 
 instance Ord Cookie where
diff --git a/http-client.cabal b/http-client.cabal
--- a/http-client.cabal
+++ b/http-client.cabal
@@ -1,5 +1,5 @@
 name:                http-client
-version:             0.4.22.1
+version:             0.4.23
 synopsis:            An HTTP client engine, intended as a base layer for more user-friendly packages.
 description:         Hackage documentation generation is not reliable. For up to date documentation, please see: <http://www.stackage.org/package/http-client>.
 homepage:            https://github.com/snoyberg/http-client
@@ -99,6 +99,7 @@
                        Network.HTTP.Client.HeadersSpec
                        Network.HTTP.Client.RequestSpec
                        Network.HTTP.Client.RequestBodySpec
+                       Network.HTTP.Client.CookieSpec
   build-depends:       base
                      , http-client
                      , hspec
diff --git a/test-nonet/Network/HTTP/Client/CookieSpec.hs b/test-nonet/Network/HTTP/Client/CookieSpec.hs
new file mode 100644
--- /dev/null
+++ b/test-nonet/Network/HTTP/Client/CookieSpec.hs
@@ -0,0 +1,27 @@
+{-# LANGUAGE OverloadedStrings #-}
+module Network.HTTP.Client.CookieSpec where
+
+import           Data.Time.Clock
+import           Network.HTTP.Client.Internal
+import           Network.HTTP.Types
+import           Test.Hspec
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = describe "CookieSpec" $ do
+    it "cookie equality - case insensitive Eq" $ do
+      now <- getCurrentTime
+      let cookie1 = Cookie "test" "value" now "doMain.Org" "/" now now False False False False
+          cookie2 = Cookie "test" "value" now "DOMAIn.ORg" "/" now now False False False False
+      cookie1 `shouldBe` cookie2
+
+    it "domainMatches - case insensitive" $ do
+      domainMatches "www.org" "www.org" `shouldBe` True
+      domainMatches "wWw.OrG" "Www.oRG" `shouldBe` True
+      domainMatches "wxw.OrG" "Www.oRG" `shouldBe` False
+
+    it "domainMatches - case insensitive, partial" $ do
+      domainMatches "www.org" "xxx.www.org" `shouldBe` False
+      domainMatches "xxx.www.org" "WWW.ORG" `shouldBe` True