diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for http3
 
+## 0.0.6
+
+* Rescuing GHC 9.0 for testing.
+
 ## 0.0.5
 
 * Supporting http2 v4.2.0.
diff --git a/http3.cabal b/http3.cabal
--- a/http3.cabal
+++ b/http3.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               http3
-version:            0.0.5
+version:            0.0.6
 license:            BSD-3-Clause
 license-file:       LICENSE
 maintainer:         Kazu Yamamoto <kazu@iij.ad.jp>
diff --git a/test/HTTP3/Error.hs b/test/HTTP3/Error.hs
--- a/test/HTTP3/Error.hs
+++ b/test/HTTP3/Error.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
 
 module HTTP3.Error (
     h3ErrorSpec
@@ -34,6 +35,7 @@
       _                                       -> H3.run conn cconf conf client
   where
     us = ms * 1000
+    client :: H3.Client ()
     client sendRequest = do
         let req = H3.requestNoBody methodGet "/" []
         ret <- sendRequest req $ \_rsp -> return ()