diff --git a/Network/Wai.hs b/Network/Wai.hs
--- a/Network/Wai.hs
+++ b/Network/Wai.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE Rank2Types #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE ExistentialQuantification #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-|
@@ -61,7 +62,11 @@
 import Data.Text (Text)
 import Data.ByteString.Lazy.Char8 () -- makes it easier to use responseLBS
 import Blaze.ByteString.Builder (fromByteString)
+#if MIN_VERSION_vault(0,3,0)
+import Data.Vault.Lazy (Vault)
+#else
 import Data.Vault (Vault)
+#endif
 import Data.Word (Word64)
 
 -- | Information on the request sent by the client. This abstracts away the
diff --git a/wai.cabal b/wai.cabal
--- a/wai.cabal
+++ b/wai.cabal
@@ -1,5 +1,5 @@
 Name:                wai
-Version:             1.4.0.1
+Version:             1.4.0.2
 Synopsis:            Web Application Interface.
 Description:         Provides a common protocol for communication between web applications and web servers.
 License:             MIT
@@ -25,6 +25,6 @@
                    , http-types                >= 0.7
                    , text                      >= 0.7
                    , transformers              >= 0.2.2
-                   , vault                     >= 0.1      && < 0.3
+                   , vault                     >= 0.1      && < 0.4
   Exposed-modules:   Network.Wai
   ghc-options:       -Wall