diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for http3
 
+## 0.0.8
+
+* Using http2 v5.1.
+
 ## 0.0.7
 
 * Supporting http2 v5.0.
diff --git a/Network/HTTP3/Client.hs b/Network/HTTP3/Client.hs
--- a/Network/HTTP3/Client.hs
+++ b/Network/HTTP3/Client.hs
@@ -63,6 +63,7 @@
 ) where
 
 import Control.Concurrent
+import qualified Data.ByteString.Char8 as C8
 import Data.IORef
 import Network.HTTP2.Client (Authority, Client, Scheme)
 import qualified Network.HTTP2.Client as H2
@@ -130,7 +131,7 @@
     let hdr = H2.outObjHeaders outobj
         hdr' =
             (":scheme", scm)
-                : (":authority", auth)
+                : (":authority", C8.pack auth)
                 : hdr
     E.bracket (newStream ctx) closeStream $ \strm -> do
         sendHeader ctx strm th hdr'
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:            0.0.7
+version:            0.0.8
 license:            BSD-3-Clause
 license-file:       LICENSE
 maintainer:         Kazu Yamamoto <kazu@iij.ad.jp>
@@ -81,7 +81,7 @@
         bytestring,
         case-insensitive,
         containers,
-        http2 >=5.0 && <5.1,
+        http2 >=5.1 && <5.2,
         http-types,
         network,
         network-byte-order,