diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,10 +1,16 @@
 # ChangeLog for http2
 
+## 5.4.3
+
+* auxSendInformational: gate usage with CPP to http-semantics >= 0.4.1
+  [#170](https://github.com/kazu-yamamoto/http2/pull/170)
+
 ## 5.4.2
 
 * Support informational (1xx) responses, e.g. 103 Early Hints. Servers can send
   them via `auxSendInformational`; clients can observe them via the new
   `confOnInformational` callback in `Config`.
+  [#168](https://github.com/kazu-yamamoto/http2/pull/168)
 
 ## 5.4.1
 
diff --git a/Network/HTTP2/Server/Worker.hs b/Network/HTTP2/Server/Worker.hs
--- a/Network/HTTP2/Server/Worker.hs
+++ b/Network/HTTP2/Server/Worker.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RecordWildCards #-}
 
@@ -6,7 +7,6 @@
 ) where
 
 import Control.Concurrent.STM
-import qualified Data.ByteString.Char8 as C8
 import Data.IORef
 import Network.HTTP.Semantics
 import Network.HTTP.Semantics.IO
@@ -19,6 +19,10 @@
 import Network.HTTP2.Frame
 import Network.HTTP2.H2
 
+#if MIN_VERSION_http_semantics(0,4,1)
+import qualified Data.ByteString.Char8 as C8
+#endif
+
 ----------------------------------------------------------------
 
 runServer :: Config -> Server -> Launch
@@ -30,7 +34,9 @@
                     { auxTimeHandle = th
                     , auxMySockAddr = mySockAddr
                     , auxPeerSockAddr = peerSockAddr
+#if MIN_VERSION_http_semantics(0,4,1)
                     , auxSendInformational = sendInformational ctx strm
+#endif
                     }
             request = Request req'
         lc <- newLoopCheck strm Nothing
@@ -50,6 +56,7 @@
 
 ----------------------------------------------------------------
 
+#if MIN_VERSION_http_semantics(0,4,1)
 -- | Send an informational (1xx) response, e.g. 103 Early Hints, on the given
 --   stream ahead of the final response. This is wired into 'auxSendInformational'
 --   so that a server (or WAI handler via Warp) can emit early hints. It blocks
@@ -60,6 +67,7 @@
     lc <- newLoopCheck strm Nothing
     let hdr = (":status", C8.pack (show (statusCode st))) : hdrs
     syncWithSender ctx strm (OInformational hdr) lc
+#endif
 
 ----------------------------------------------------------------
 
diff --git a/http2.cabal b/http2.cabal
--- a/http2.cabal
+++ b/http2.cabal
@@ -1,6 +1,6 @@
 cabal-version:      >=1.10
 name:               http2
-version:            5.4.2
+version:            5.4.3
 license:            BSD3
 license-file:       LICENSE
 maintainer:         Kazu Yamamoto <kazu@iij.ad.jp>