diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 0.5.3.3
+
+* Add missing colon in Host header [#235](https://github.com/snoyberg/http-client/pull/235)
+
 ## 0.5.3.2
 
 * Minor doc updates
diff --git a/Network/HTTP/Client/Manager.hs b/Network/HTTP/Client/Manager.hs
--- a/Network/HTTP/Client/Manager.hs
+++ b/Network/HTTP/Client/Manager.hs
@@ -419,7 +419,7 @@
                 let ultHost = host req
                     ultPort = port req
                     proxyAuthorizationHeader = maybe "" (\h' -> S8.concat ["Proxy-Authorization: ", h', "\r\n"]) . lookup "Proxy-Authorization" $ requestHeaders req
-                    hostHeader = S8.concat ["Host: ", ultHost, (S8.pack $ show ultPort), "\r\n"]
+                    hostHeader = S8.concat ["Host: ", ultHost, ":", (S8.pack $ show ultPort), "\r\n"]
                     connstr = S8.concat
                         [ "CONNECT "
                         , ultHost
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:             0.5.3.2
+version:             0.5.3.3
 synopsis:            An HTTP client engine
 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