diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 0.5.1
+
+* Add the `Partitioned` cookie attribute.
+
 ## 0.5.0
 
 * Remove surrounding double quotes from cookie values when parsing [#31](https://github.com/snoyberg/cookie/pull/31)
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,5 +1,5 @@
 ## cookie
 
-[![Build Status](https://travis-ci.org/snoyberg/cookie.svg?branch=master)](https://travis-ci.org/snoyberg/cookie)
+[![Build Status](https://github.com/snoyberg/cookie/actions/workflows/tests.yaml/badge.svg)](https://github.com/snoyberg/cookie/actions)
 
 HTTP cookie parsing and rendering
diff --git a/Setup.lhs b/Setup.lhs
deleted file mode 100644
--- a/Setup.lhs
+++ /dev/null
@@ -1,8 +0,0 @@
-#!/usr/bin/env runhaskell
-
-> module Main where
-> import Distribution.Simple
-> import System.Cmd (system)
-
-> main :: IO ()
-> main = defaultMain
diff --git a/Web/Cookie.hs b/Web/Cookie.hs
--- a/Web/Cookie.hs
+++ b/Web/Cookie.hs
@@ -13,6 +13,7 @@
     , setCookieHttpOnly
     , setCookieSecure
     , setCookieSameSite
+    , setCookiePartitioned
     , SameSiteOption
     , sameSiteLax
     , sameSiteStrict
@@ -55,7 +56,7 @@
 import Data.Text (Text)
 import Data.Text.Encoding (encodeUtf8Builder, decodeUtf8With)
 import Data.Text.Encoding.Error (lenientDecode)
-import Data.Maybe (isJust)
+import Data.Maybe (isJust, fromMaybe, listToMaybe)
 import Data.Default.Class (Default (def))
 import Control.DeepSeq (NFData (rnf))
 
@@ -73,19 +74,31 @@
 
 type Cookies = [(S.ByteString, S.ByteString)]
 
+semicolon :: Word8
+semicolon = 59
+
+equalsSign :: Word8
+equalsSign = 61
+
+space :: Word8
+space = 32
+
+doubleQuote :: Word8
+doubleQuote = 34
+
 -- | Decode the value of a \"Cookie\" request header into key/value pairs.
 parseCookies :: S.ByteString -> Cookies
 parseCookies s
   | S.null s = []
   | otherwise =
-    let (x, y) = breakDiscard 59 s -- semicolon
+    let (x, y) = breakDiscard semicolon s
      in parseCookie x : parseCookies y
 
 parseCookie :: S.ByteString -> (S.ByteString, S.ByteString)
 parseCookie s =
-    let (key, value) = breakDiscard 61 s -- equals sign
-        key' = S.dropWhile (== 32) key -- space
-        value' = dropEnds 34 value -- double quote
+    let (key, value) = breakDiscard equalsSign s
+        key' = S.dropWhile (== space) key
+        value' = dropEnds doubleQuote value
      in (key', value')
 
 breakDiscard :: Word8 -> S.ByteString -> (S.ByteString, S.ByteString)
@@ -145,6 +158,7 @@
     , setCookieHttpOnly :: Bool -- ^ Marks the cookie as "HTTP only", i.e. not accessible from Javascript. Default value: @False@
     , setCookieSecure :: Bool -- ^ Instructs the browser to only send the cookie over HTTPS. Default value: @False@
     , setCookieSameSite :: Maybe SameSiteOption -- ^ The "same site" policy of the cookie, i.e. whether it should be sent with cross-site requests. Default value: @Nothing@
+    , setCookiePartitioned :: Bool -- ^ Cookies marked Partitioned are double-keyed: by the origin that sets them and the origin of the top-level page. Default value: @False@
     }
     deriving (Eq, Show)
 
@@ -173,7 +187,7 @@
 sameSiteNone = None
 
 instance NFData SetCookie where
-    rnf (SetCookie a b c d e f g h i) =
+    rnf (SetCookie a b c d e f g h i j) =
         a `seq`
         b `seq`
         rnfMBS c `seq`
@@ -182,7 +196,8 @@
         rnfMBS f `seq`
         rnf g `seq`
         rnf h `seq`
-        rnf i
+        rnf i `seq`
+        rnf j
       where
         -- For backwards compatibility
         rnfMBS Nothing = ()
@@ -206,6 +221,7 @@
     , setCookieHttpOnly = False
     , setCookieSecure   = False
     , setCookieSameSite = Nothing
+    , setCookiePartitioned = False
     }
 
 renderSetCookie :: SetCookie -> Builder
@@ -223,7 +239,7 @@
                   byteString (formatCookieExpires e)
     , case setCookieMaxAge sc of
         Nothing -> mempty
-        Just ma -> byteStringCopy"; Max-Age=" `mappend`
+        Just ma -> byteStringCopy "; Max-Age=" `mappend`
                    byteString (formatCookieMaxAge ma)
     , case setCookieDomain sc of
         Nothing -> mempty
@@ -240,6 +256,9 @@
         Just Lax -> byteStringCopy "; SameSite=Lax"
         Just Strict -> byteStringCopy "; SameSite=Strict"
         Just None -> byteStringCopy "; SameSite=None"
+    , if setCookiePartitioned sc
+        then byteStringCopy "; Partitioned"
+        else mempty
     ]
 
 -- | @since 0.4.6
@@ -249,7 +268,7 @@
 parseSetCookie :: S.ByteString -> SetCookie
 parseSetCookie a = SetCookie
     { setCookieName = name
-    , setCookieValue = dropEnds 34 value -- double quote
+    , setCookieValue = dropEnds doubleQuote value
     , setCookiePath = lookup "path" flags
     , setCookieExpires =
         lookup "expires" flags >>= parseCookieExpires
@@ -263,13 +282,14 @@
         Just "Strict" -> Just Strict
         Just "None" -> Just None
         _ -> Nothing
+    , setCookiePartitioned = isJust $ lookup "partitioned" flags
     }
   where
-    pairs = map (parsePair . dropSpace) $ S.split 59 a ++ [S8.empty] -- 59 = semicolon
-    (name, value) = head pairs
-    flags = map (first (S8.map toLower)) $ tail pairs
-    parsePair = breakDiscard 61 -- equals sign
-    dropSpace = S.dropWhile (== 32) -- space
+    pairs = map (parsePair . dropSpace) $ S.split semicolon a
+    (name, value) = fromMaybe mempty $ listToMaybe pairs
+    flags = map (first (S8.map toLower)) $ drop 1 pairs
+    parsePair = breakDiscard equalsSign
+    dropSpace = S.dropWhile (== space)
 
 expiresFormat :: String
 expiresFormat = "%a, %d-%b-%Y %X GMT"
diff --git a/cookie.cabal b/cookie.cabal
--- a/cookie.cabal
+++ b/cookie.cabal
@@ -1,5 +1,6 @@
+cabal-version:   >= 1.10
 name:            cookie
-version:         0.5.0
+version:         0.5.1
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -8,9 +9,8 @@
 description:     Hackage documentation generation is not reliable. For up to date documentation, please see: <https://www.stackage.org/package/cookie>.
 category:        Web, Yesod
 stability:       Stable
-cabal-version:   >= 1.10
 build-type:      Simple
-homepage:        http://github.com/snoyberg/cookie
+homepage:        https://github.com/snoyberg/cookie
 extra-source-files: README.md ChangeLog.md
 
 library
@@ -42,4 +42,4 @@
 
 source-repository head
   type:     git
-  location: git://github.com/snoyberg/cookie.git
+  location: https://github.com/snoyberg/cookie.git
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -1,18 +1,19 @@
-import Test.Tasty (defaultMain, testGroup)
+{-# OPTIONS_GHC -Wno-orphans #-}
+module Main where
+
+import Test.Tasty (defaultMain, testGroup, TestTree)
 import Test.Tasty.QuickCheck (testProperty)
 import Test.Tasty.HUnit (testCase)
 import Test.QuickCheck
 import Test.HUnit ((@=?), Assertion)
 
 import Web.Cookie
-import Data.ByteString.Builder (Builder, word8, toLazyByteString)
+import Data.ByteString.Builder (Builder, toLazyByteString)
 import qualified Data.ByteString as S
 import qualified Data.ByteString.Char8 as S8
 import qualified Data.ByteString.Lazy as L
 import Data.Word (Word8)
-import Data.Monoid (mconcat)
 import Control.Arrow ((***))
-import Control.Applicative ((<$>), (<*>))
 import Data.Time (UTCTime (UTCTime), toGregorian)
 import qualified Data.Text as T
 
@@ -54,7 +55,7 @@
     show (Char' w) = [toEnum $ fromEnum w]
     showList = (++) . show . concatMap show
 instance Arbitrary Char' where
-    arbitrary = fmap (Char' . toEnum) $ choose (62, 125)
+    arbitrary = Char' . toEnum <$> choose (62, 125)
 newtype SameSiteOption' = SameSiteOption' { unSameSiteOption' :: SameSiteOption }
 instance Arbitrary SameSiteOption' where
   arbitrary = fmap SameSiteOption' (elements [sameSiteLax, sameSiteStrict, sameSiteNone])
@@ -74,6 +75,7 @@
         httponly <- arbitrary
         secure <- arbitrary
         sameSite <- fmap (fmap unSameSiteOption') arbitrary
+        partitioned <- arbitrary
         return def
             { setCookieName = name
             , setCookieValue = value
@@ -83,6 +85,7 @@
             , setCookieHttpOnly = httponly
             , setCookieSecure = secure
             , setCookieSameSite = sameSite
+            , setCookiePartitioned = partitioned
             }
 
 caseParseCookies :: Assertion
@@ -91,16 +94,20 @@
         expected = [("a", "a1"), ("b", "b2"), ("c", "c3")]
     map (S8.pack *** S8.pack) expected @=? parseCookies input
 
+-- TODO: Use `Year` from Data.Time when we'll remove support for GHC <9.2
+type Year = Integer
+
 -- Tests for two digit years, see:
 --
 -- https://github.com/snoyberg/cookie/issues/5
+twoDigit :: Year -> Year -> TestTree
 twoDigit x y =
     testCase ("year " ++ show x) (y @=? year)
   where
     (year, _, _) = toGregorian day
     day =
         case setCookieExpires sc of
-            Just (UTCTime day _) -> day
+            Just (UTCTime day' _) -> day'
             Nothing -> error $ "setCookieExpires == Nothing for: " ++ show str
     sc = parseSetCookie str
     str = S8.pack $ concat