diff --git a/happstack-server.cabal b/happstack-server.cabal
--- a/happstack-server.cabal
+++ b/happstack-server.cabal
@@ -1,5 +1,5 @@
 Name:                happstack-server
-Version:             7.3.0
+Version:             7.3.1
 Synopsis:            Web related tools and services.
 Description:         Happstack Server provides an HTTP server and a rich set of functions for routing requests, handling query parameters, generating responses, working with cookies, serving files, and more. For in-depth documentation see the Happstack Crash Course <http://happstack.com/docs/crashcourse/index.html>
 License:             BSD3
diff --git a/src/Happstack/Server/Internal/Types.hs b/src/Happstack/Server/Internal/Types.hs
--- a/src/Happstack/Server/Internal/Types.hs
+++ b/src/Happstack/Server/Internal/Types.hs
@@ -405,7 +405,7 @@
 -- type.  Does not force the key to be in lowercase or guarantee that the given key and the key in the HeaderPair will match.
 addHeaderUnsafe :: HasHeaders r => ByteString -> HeaderPair -> r -> r
 addHeaderUnsafe key val = updateHeaders (M.insertWith join key val)
-    where join (HeaderPair k vs1) (HeaderPair _ vs2) = HeaderPair k (vs1++vs2)
+    where join (HeaderPair k vs1) (HeaderPair _ vs2) = HeaderPair k (vs2++vs1)
 
 -- | Creates a Response with the given Int as the status code and the provided
 -- String as the body of the Response
diff --git a/tests/Happstack/Server/Tests.hs b/tests/Happstack/Server/Tests.hs
--- a/tests/Happstack/Server/Tests.hs
+++ b/tests/Happstack/Server/Tests.hs
@@ -31,6 +31,7 @@
                                 , multipart
                                 , compressFilterResponseTest
                                 , matchMethodTest
+                                , cookieHeaderOrderTest
                                 ]
 
 cookieParserTest :: Test
@@ -142,6 +143,21 @@
        msum [ dir "response" $ ok (toResponse "compress Response")
             , dir "sendfile" $ ok (sendFileResponse "text/plain" "/dev/null" Nothing 0 100)
             ]
+
+cookieHeaderOrderTestHandler :: ServerPart Response
+cookieHeaderOrderTestHandler = do
+  expireCookie "thecookie"
+  addCookie Session $ mkCookie "thecookie" "value"
+  ok $ toResponse $ "works"
+
+cookieHeaderOrderTest :: Test
+cookieHeaderOrderTest =
+  "cookie header order test" ~:
+    do req <- mkRequest GET "/" [] Map.empty L.empty
+       res <- simpleHTTP'' cookieHeaderOrderTestHandler req
+       let Just pair = (Map.lookup (B.pack "set-cookie") (rsHeaders res))
+       assertEqual "Add cookie wins" False $ B.isInfixOf (B.pack "Max-Age=0")
+                                                         (last $ hValue pair)
 
 uncompressedResponse :: Test
 uncompressedResponse =