diff --git a/Network/HTTP/Conduit.hs b/Network/HTTP/Conduit.hs
--- a/Network/HTTP/Conduit.hs
+++ b/Network/HTTP/Conduit.hs
@@ -31,7 +31,11 @@
 --
 -- * Content-Length
 --
--- * Host
+-- Note: In previous versions, the Host header would be set by this module in
+-- all cases. Starting from 1.6.1, if a Host header is present in
+-- @requestHeaders@, it will be used in place of the header this module would
+-- have generated. This can be useful for calling a server which utilizes
+-- virtual hosting.
 --
 -- Any network code on Windows requires some initialization, and the network
 -- library provides withSocketsDo to perform it. Therefore, proper usage of
diff --git a/Network/HTTP/Conduit/Request.hs b/Network/HTTP/Conduit/Request.hs
--- a/Network/HTTP/Conduit/Request.hs
+++ b/Network/HTTP/Conduit/Request.hs
@@ -248,7 +248,10 @@
             Just "" -> filter (\(k, _) -> k /= "Accept-Encoding")
             Just _ -> id
 
-    hostHeader = (("Host", hh):)
+    hostHeader x =
+        case lookup "Host" x of
+            Nothing -> ("Host", hh) : x
+            Just{} -> x
 
     headerPairs :: W.RequestHeaders
     headerPairs = hostHeader
diff --git a/http-conduit.cabal b/http-conduit.cabal
--- a/http-conduit.cabal
+++ b/http-conduit.cabal
@@ -1,5 +1,5 @@
 name:            http-conduit
-version:         1.6.0.4
+version:         1.6.1
 license:         BSD3
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -79,7 +79,7 @@
     cpp-options:   -DDEBUG
     build-depends: base >= 4 && < 5
                  , HUnit
-                 , hspec
+                 , hspec >= 1.3
                  , bytestring
                  , transformers
                  , failure
diff --git a/test/main.hs b/test/main.hs
--- a/test/main.hs
+++ b/test/main.hs
@@ -1,9 +1,8 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-import Test.Hspec.Monadic
+import Test.Hspec
 import qualified Data.ByteString as S
 import qualified Data.ByteString.Char8 as S8
-import Test.Hspec.HUnit ()
 import Test.HUnit
 import Network.Wai hiding (requestBody)
 import qualified Network.Wai
@@ -65,7 +64,7 @@
           redir3 = (mk (fromString "Location"), fromString "/redir3")
 
 main :: IO ()
-main = hspecX $ do
+main = hspec $ do
     cookieTest
     describe "simpleHttp" $ do
         it "gets homepage" $ do