diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,10 @@
 # ChangeLog
 
+## 0.2.18
+
+* Don't print debug information on stdout as a daemon has already
+  closed it.
+
 ## 0.2.17
 
 * Using waitReadSocketSTM properly.
diff --git a/Network/QUIC/Server/Reader.hs b/Network/QUIC/Server/Reader.hs
--- a/Network/QUIC/Server/Reader.hs
+++ b/Network/QUIC/Server/Reader.hs
@@ -187,10 +187,7 @@
             mapM_ switch cpckts
             loop
 
-    doDebug = isJust $ scDebugLog conf
-    logAction msg
-        | doDebug = stdoutLogger ("dispatch(er): " <> msg)
-        | otherwise = return ()
+    logAction _msg = return ()
 
     safeRecv rcv = do
         ex <- E.try $ windowsThreadBlockHack rcv
diff --git a/Network/QUIC/Server/Run.hs b/Network/QUIC/Server/Run.hs
--- a/Network/QUIC/Server/Run.hs
+++ b/Network/QUIC/Server/Run.hs
@@ -13,7 +13,6 @@
 import Control.Concurrent.STM
 import qualified Control.Exception as E
 import qualified Network.Socket as NS
-import System.Log.FastLogger hiding (check)
 
 import Network.QUIC.Closer
 import Network.QUIC.Common
@@ -50,10 +49,7 @@
             st <- readTVar stvar
             check $ st == Stopped
   where
-    doDebug = isJust $ scDebugLog conf
-    debugLog msg
-        | doDebug = stdoutLogger ("run: " <> msg)
-        | otherwise = return ()
+    debugLog _msg = return ()
     setup stvar = do
         dispatch <- newDispatch conf
         let forkConn acc = void $ forkIO (runServer conf server dispatch stvar acc)
@@ -79,10 +75,7 @@
             st <- readTVar stvar
             check $ st == Stopped
   where
-    doDebug = isJust $ scDebugLog conf
-    debugLog msg
-        | doDebug = stdoutLogger ("run: " <> msg)
-        | otherwise = return ()
+    debugLog _msg = return ()
     setup stvar = do
         dispatch <- newDispatch conf
         let forkConn acc = void $ forkIO (runServer conf server dispatch stvar acc)
@@ -144,9 +137,7 @@
         let conn = connResConnection connRes
         setDead conn
         freeResources conn
-    debugLog conn msg = do
-        connDebugLog conn ("runServer: " <> msg)
-        qlogDebug conn $ Debug $ toLogStr msg
+    debugLog _conn _msg = return ()
 
 createServerConnection
     :: ServerConfig
diff --git a/quic.cabal b/quic.cabal
--- a/quic.cabal
+++ b/quic.cabal
@@ -1,6 +1,6 @@
 cabal-version:      >=1.10
 name:               quic
-version:            0.2.17
+version:            0.2.18
 license:            BSD3
 license-file:       LICENSE
 maintainer:         kazu@iij.ad.jp