diff --git a/ChangeLog.md b/ChangeLog.md
new file mode 100644
--- /dev/null
+++ b/ChangeLog.md
@@ -0,0 +1,9 @@
+# ChangeLog for wai-logger
+
+## 2.5.1
+
+* Security: request-derived fields (IP from headers, user, method,
+  path, Referer, User-Agent) are now escaped like Apache's
+  `ap_escape_logitem` to prevent log injection.
+* The IP taken from X-Real-IP or X-Forwarded-For is now the first
+  token only.
diff --git a/Network/Wai/Logger.hs b/Network/Wai/Logger.hs
--- a/Network/Wai/Logger.hs
+++ b/Network/Wai/Logger.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE CPP   #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE GADTs #-}
 
 -- | Apache style logger for WAI applications.
@@ -30,34 +30,38 @@
 -- >     pong = "PONG"
 -- >     msg = byteString pong
 -- >     len = fromIntegral $ BS.length pong
-
 module Network.Wai.Logger (
-  -- * High level functions
-    ApacheLogger
-  , withStdoutLogger
-  , ServerPushLogger
-  -- * Creating a logger
-  , ApacheLoggerActions
-  , apacheLogger
-  , serverpushLogger
-  , logRotator
-  , logRemover
-  , initLoggerUser
-  , initLogger
-  -- * Types
-  , IPAddrSource(..)
-  , LogType'(..), LogType
-  , FileLogSpec(..)
-  -- * Utilities
-  , showSockAddr
-  , logCheck
-  -- * Backward compability
-  , clockDateCacher
-  , ZonedDate
-  , DateCacheGetter
-  , DateCacheUpdater
-  ) where
+    -- * High level functions
+    ApacheLogger,
+    withStdoutLogger,
+    ServerPushLogger,
 
+    -- * Creating a logger
+    ApacheLoggerActions,
+    apacheLogger,
+    serverpushLogger,
+    logRotator,
+    logRemover,
+    initLoggerUser,
+    initLogger,
+
+    -- * Types
+    IPAddrSource (..),
+    LogType' (..),
+    LogType,
+    FileLogSpec (..),
+
+    -- * Utilities
+    showSockAddr,
+    logCheck,
+
+    -- * Backward compability
+    clockDateCacher,
+    ZonedDate,
+    DateCacheGetter,
+    DateCacheUpdater,
+) where
+
 #if __GLASGOW_HASKELL__ < 709
 import Control.Applicative ((<$>))
 #endif
@@ -97,35 +101,44 @@
 type ServerPushLogger = Request -> ByteString -> Integer -> IO ()
 
 -- | Function set of Apache style logger.
-data ApacheLoggerActions = ApacheLoggerActions {
-    -- | The Apache logger.
-    apacheLogger :: ApacheLogger
-    -- | The HTTP/2 server push logger.
-  , serverpushLogger :: ServerPushLogger
-    -- | This is obsoleted. Rotation is done on-demand.
+data ApacheLoggerActions = ApacheLoggerActions
+    { apacheLogger :: ApacheLogger
+    -- ^ The Apache logger.
+    , serverpushLogger :: ServerPushLogger
+    -- ^ The HTTP/2 server push logger.
+    , logRotator :: IO ()
+    -- ^ This is obsoleted. Rotation is done on-demand.
     --   So, this is now an empty action.
-  , logRotator :: IO ()
-    -- | Removing resources relating to Apache logger.
+    , logRemover :: IO ()
+    -- ^ Removing resources relating to Apache logger.
     --   E.g. flushing and deallocating internal buffers.
-  , logRemover :: IO ()
-  }
+    }
 
 ----------------------------------------------------------------
 
 -- | Creating 'ApacheLogger' according to 'LogType'.
-initLoggerUser :: ToLogStr user => Maybe (Request -> Maybe user) -> IPAddrSource -> LogType -> IO FormattedTime
-               -> IO ApacheLoggerActions
+initLoggerUser
+    :: ToLogStr user
+    => Maybe (Request -> Maybe user)
+    -> IPAddrSource
+    -> LogType
+    -> IO FormattedTime
+    -> IO ApacheLoggerActions
 initLoggerUser ugetter ipsrc typ tgetter = do
     (fl, cleanUp) <- newFastLogger typ
-    return $ ApacheLoggerActions {
-        apacheLogger     = apache fl ipsrc ugetter tgetter
-      , serverpushLogger = serverpush fl ipsrc ugetter tgetter
-      , logRotator       = return ()
-      , logRemover       = cleanUp
-      }
+    return $
+        ApacheLoggerActions
+            { apacheLogger = apache fl ipsrc ugetter tgetter
+            , serverpushLogger = serverpush fl ipsrc ugetter tgetter
+            , logRotator = return ()
+            , logRemover = cleanUp
+            }
 
-initLogger :: IPAddrSource -> LogType -> IO FormattedTime
-           -> IO ApacheLoggerActions
+initLogger
+    :: IPAddrSource
+    -> LogType
+    -> IO FormattedTime
+    -> IO ApacheLoggerActions
 initLogger = initLoggerUser nouser
   where
     nouser :: Maybe (Request -> Maybe ByteString)
@@ -133,22 +146,34 @@
 
 --- | Checking if a log file can be written if 'LogType' is 'LogFileNoRotate' or 'LogFile'.
 logCheck :: LogType -> IO ()
-logCheck LogNone          = return ()
-logCheck (LogStdout _)    = return ()
-logCheck (LogStderr _)    = return ()
-logCheck (LogFileNoRotate fp _)      = check fp
-logCheck (LogFile spec _)            = check (log_file spec)
+logCheck LogNone = return ()
+logCheck (LogStdout _) = return ()
+logCheck (LogStderr _) = return ()
+logCheck (LogFileNoRotate fp _) = check fp
+logCheck (LogFile spec _) = check (log_file spec)
 logCheck (LogFileTimedRotate spec _) = check (timed_log_file spec)
 logCheck (LogCallback _ _) = return ()
 
 ----------------------------------------------------------------
 
-apache :: ToLogStr user => (LogStr -> IO ()) -> IPAddrSource -> Maybe (Request -> Maybe user) -> IO FormattedTime -> ApacheLogger
+apache
+    :: ToLogStr user
+    => (LogStr -> IO ())
+    -> IPAddrSource
+    -> Maybe (Request -> Maybe user)
+    -> IO FormattedTime
+    -> ApacheLogger
 apache cb ipsrc userget dateget req st mlen = do
     zdata <- dateget
     cb (apacheLogStr ipsrc (justGetUser userget) zdata req st mlen)
 
-serverpush :: ToLogStr user => (LogStr -> IO ()) -> IPAddrSource -> Maybe (Request -> Maybe user) -> IO FormattedTime -> ServerPushLogger
+serverpush
+    :: ToLogStr user
+    => (LogStr -> IO ())
+    -> IPAddrSource
+    -> Maybe (Request -> Maybe user)
+    -> IO FormattedTime
+    -> ServerPushLogger
 serverpush cb ipsrc userget dateget req path size = do
     zdata <- dateget
     cb (serverpushLogStr ipsrc (justGetUser userget) zdata req path size)
@@ -178,4 +203,4 @@
 
 justGetUser :: Maybe (Request -> Maybe user) -> (Request -> Maybe user)
 justGetUser (Just getter) = getter
-justGetUser Nothing       = \_ -> Nothing
+justGetUser Nothing = \_ -> Nothing
diff --git a/Network/Wai/Logger/Apache.hs b/Network/Wai/Logger/Apache.hs
--- a/Network/Wai/Logger/Apache.hs
+++ b/Network/Wai/Logger/Apache.hs
@@ -1,10 +1,12 @@
-{-# LANGUAGE OverloadedStrings, CPP, TupleSections #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TupleSections #-}
 
 module Network.Wai.Logger.Apache (
-    IPAddrSource(..)
-  , apacheLogStr
-  , serverpushLogStr
-  ) where
+    IPAddrSource (..),
+    apacheLogStr,
+    serverpushLogStr,
+) where
 
 #ifndef MIN_VERSION_base
 #define MIN_VERSION_base(x,y,z) 1
@@ -13,10 +15,17 @@
 #define MIN_VERSION_wai(x,y,z) 1
 #endif
 
+import qualified Data.ByteString as B
 import Data.ByteString.Char8 (ByteString)
 import qualified Data.ByteString.Char8 as BS
+import qualified Data.ByteString.Internal as BI
+import qualified Data.ByteString.Unsafe as BU
+import Data.Char (isSpace)
 import Data.List (find)
 import Data.Maybe (fromMaybe)
+import Data.Word (Word8)
+import Foreign.Ptr (Ptr)
+import Foreign.Storable (pokeByteOff)
 #if MIN_VERSION_base(4,5,0)
 import Data.Monoid ((<>), First (..))
 #else
@@ -24,7 +33,7 @@
 #endif
 import Network.HTTP.Types (Status, statusCode)
 import Network.HTTP.Types.Header (HeaderName)
-import Network.Wai (Request(..))
+import Network.Wai (Request (..))
 import Network.Wai.Logger.IP
 import System.Log.FastLogger
 
@@ -33,57 +42,65 @@
 -- >>> import Network.Wai (defaultRequest)
 
 -- | Source from which the IP source address of the client is obtained.
-data IPAddrSource =
-  -- | From the peer address of the HTTP connection.
-    FromSocket
-  -- | From @X-Real-IP@ or @X-Forwarded-For@ in the HTTP header.
-  --
-  -- This picks either @X-Real-IP@ or @X-Forwarded-For@ depending on which of these
-  -- headers comes first in the ordered list of request headers.
-  --
-  -- If the @X-Forwarded-For@ header is picked, the value will be assumed to be a
-  -- comma-separated list of IP addresses.  The value will be parsed, and the
-  -- left-most IP address will be used (which is mostly likely to be the actual
-  -- client IP address).
-  | FromHeader
-  -- | From a custom HTTP header, useful in proxied environment.
-  --
-  -- The header value will be assumed to be a comma-separated list of IP
-  -- addresses.  The value will be parsed, and the left-most IP address will be
-  -- used (which is mostly likely to be the actual client IP address).
-  --
-  -- Note that this still works as expected for a single IP address.
-  | FromHeaderCustom [HeaderName]
-  -- | Just like 'FromHeader', but falls back on the peer address if header is not found.
-  | FromFallback
-  -- | This gives you the most flexibility to figure out the IP source address
-  -- from the 'Request'.  The returned 'ByteString' is used as the IP source
-  -- address.
-  | FromRequest (Request -> ByteString)
+data IPAddrSource
+    = -- | From the peer address of the HTTP connection.
+      FromSocket
+    | -- | From @X-Real-IP@ or @X-Forwarded-For@ in the HTTP header.
+      --
+      -- This picks either @X-Real-IP@ or @X-Forwarded-For@ depending on which of these
+      -- headers comes first in the ordered list of request headers.
+      --
+      -- If the @X-Forwarded-For@ header is picked, the value will be assumed to be a
+      -- comma-separated list of IP addresses.  The value will be parsed, and the
+      -- left-most IP address will be used (which is mostly likely to be the actual
+      -- client IP address).
+      FromHeader
+    | -- | From a custom HTTP header, useful in proxied environment.
+      --
+      -- The header value will be assumed to be a comma-separated list of IP
+      -- addresses.  The value will be parsed, and the left-most IP address will be
+      -- used (which is mostly likely to be the actual client IP address).
+      --
+      -- Note that this still works as expected for a single IP address.
+      FromHeaderCustom [HeaderName]
+    | -- | Just like 'FromHeader', but falls back on the peer address if header is not found.
+      FromFallback
+    | -- | This gives you the most flexibility to figure out the IP source address
+      -- from the 'Request'.  The returned 'ByteString' is used as the IP source
+      -- address.
+      FromRequest (Request -> ByteString)
 
 -- | Apache style log format.
-apacheLogStr :: ToLogStr user => IPAddrSource -> (Request -> Maybe user) -> FormattedTime -> Request -> Status -> Maybe Integer -> LogStr
+apacheLogStr
+    :: ToLogStr user
+    => IPAddrSource
+    -> (Request -> Maybe user)
+    -> FormattedTime
+    -> Request
+    -> Status
+    -> Maybe Integer
+    -> LogStr
 apacheLogStr ipsrc userget tmstr req status msize =
-      toLogStr (getSourceIP ipsrc req)
-  <> " - "
-  <> maybe "-" toLogStr (userget req)
-  <> " ["
-  <> toLogStr tmstr
-  <> "] \""
-  <> toLogStr (requestMethod req)
-  <> " "
-  <> toLogStr path
-  <> " "
-  <> toLogStr (show (httpVersion req))
-  <> "\" "
-  <> toLogStr (show (statusCode status))
-  <> " "
-  <> toLogStr (maybe "-" show msize)
-  <> " \""
-  <> toLogStr (fromMaybe "" mr)
-  <> "\" \""
-  <> toLogStr (fromMaybe "" mua)
-  <> "\"\n"
+    toLogStr (escapeLogItem (getSourceIP ipsrc req))
+        <> " - "
+        <> maybe "-" escapeUser (userget req)
+        <> " ["
+        <> toLogStr tmstr
+        <> "] \""
+        <> toLogStr (escapeLogItem (requestMethod req))
+        <> " "
+        <> toLogStr (escapeLogItem path)
+        <> " "
+        <> toLogStr (show (httpVersion req))
+        <> "\" "
+        <> toLogStr (show (statusCode status))
+        <> " "
+        <> toLogStr (maybe "-" show msize)
+        <> " \""
+        <> toLogStr (escapeLogItem (fromMaybe "" mr))
+        <> "\" \""
+        <> toLogStr (escapeLogItem (fromMaybe "" mua))
+        <> "\"\n"
   where
     path = rawPathInfo req <> rawQueryString req
 #if !MIN_VERSION_base(4,5,0)
@@ -98,24 +115,32 @@
 #endif
 
 -- | HTTP/2 Push log format in the Apache style.
-serverpushLogStr :: ToLogStr user => IPAddrSource -> (Request -> Maybe user) -> FormattedTime -> Request -> ByteString -> Integer -> LogStr
+serverpushLogStr
+    :: ToLogStr user
+    => IPAddrSource
+    -> (Request -> Maybe user)
+    -> FormattedTime
+    -> Request
+    -> ByteString
+    -> Integer
+    -> LogStr
 serverpushLogStr ipsrc userget tmstr req path size =
-      toLogStr (getSourceIP ipsrc req)
-  <> " - "
-  <> maybe "-" toLogStr (userget req)
-  <> " ["
-  <> toLogStr tmstr
-  <> "] \"PUSH "
-  <> toLogStr path
-  <> " HTTP/2\" 200 "
-  <> toLogStr (show size)
-  <> " \""
-  <> toLogStr ref
-  <> "\" \""
-  <> toLogStr (fromMaybe "" mua)
-  <> "\"\n"
+    toLogStr (escapeLogItem (getSourceIP ipsrc req))
+        <> " - "
+        <> maybe "-" escapeUser (userget req)
+        <> " ["
+        <> toLogStr tmstr
+        <> "] \"PUSH "
+        <> toLogStr (escapeLogItem path)
+        <> " HTTP/2\" 200 "
+        <> toLogStr (show size)
+        <> " \""
+        <> toLogStr (escapeLogItem ref)
+        <> "\" \""
+        <> toLogStr (escapeLogItem (fromMaybe "" mua))
+        <> "\"\n"
   where
-    ref  = rawPathInfo req
+    ref = rawPathInfo req
 #if !MIN_VERSION_base(4,5,0)
     (<>) = mappend
 #endif
@@ -125,6 +150,64 @@
     mua = lookup "user-agent" $ requestHeaders req
 #endif
 
+escapeUser :: ToLogStr user => user -> LogStr
+escapeUser = toLogStr . escapeLogItem . fromLogStr . toLogStr
+
+-- | Escaping a request-derived field as Apache's @ap_escape_logitem@ does.
+--   No copy is made if nothing needs to be escaped.
+--
+-- >>> escapeLogItem "Mozilla/5.0"
+-- "Mozilla/5.0"
+-- >>> escapeLogItem "a\"b\\c\r\n\x01\x7f\xe3"
+-- "a\\\"b\\\\c\\r\\n\\x01\\x7f\\xe3"
+escapeLogItem :: ByteString -> ByteString
+escapeLogItem bs
+    | extra == 0 = bs
+    | otherwise = BI.unsafeCreate (len + extra) $ \p -> fill p 0 0
+  where
+    len = B.length bs
+    extra = B.foldl' (\n w -> n + escapeLen w) 0 bs
+    fill :: Ptr Word8 -> Int -> Int -> IO ()
+    fill p i j
+        | i >= len = return ()
+        | otherwise = do
+            let w = BU.unsafeIndex bs i
+            case escapeLen w of
+                0 -> do
+                    pokeByteOff p j w
+                    fill p (i + 1) (j + 1)
+                1 -> do
+                    pokeByteOff p j backslash
+                    pokeByteOff p (j + 1) (escapeChar w)
+                    fill p (i + 1) (j + 2)
+                _ -> do
+                    pokeByteOff p j backslash
+                    pokeByteOff p (j + 1) (0x78 :: Word8) -- 'x'
+                    pokeByteOff p (j + 2) (hex (w `div` 16))
+                    pokeByteOff p (j + 3) (hex (w `mod` 16))
+                    fill p (i + 1) (j + 4)
+    backslash = 0x5c :: Word8
+    hex :: Word8 -> Word8
+    hex n
+        | n < 10 = 0x30 + n
+        | otherwise = 0x57 + n -- lower case as Apache
+
+-- Number of extra bytes needed to escape a byte.
+escapeLen :: Word8 -> Int
+escapeLen w
+    | w == 0x22 || w == 0x5c = 1 -- '"' and '\\'
+    | w >= 0x20 && w < 0x7f = 0
+    | w >= 0x08 && w <= 0x0d && w /= 0x0c = 1 -- \b \t \n \v \r
+    | otherwise = 3
+
+escapeChar :: Word8 -> Word8
+escapeChar 0x08 = 0x62 -- b
+escapeChar 0x09 = 0x74 -- t
+escapeChar 0x0a = 0x6e -- n
+escapeChar 0x0b = 0x76 -- v
+escapeChar 0x0d = 0x72 -- r
+escapeChar w = w -- '"' and '\\'
+
 getSourceIP :: IPAddrSource -> Request -> ByteString
 getSourceIP FromSocket = getSourceFromSocket
 getSourceIP FromHeader = getSourceFromHeader
@@ -214,14 +297,19 @@
 -- >>> getSource defaultRequest { requestHeaders = [ ("X-Forwarded-For", "5.6.7.8, 10.11.12.13, 1.2.3.4") ] }
 -- Just "5.6.7.8"
 getSource :: Request -> Maybe ByteString
-getSource = getSourceFromHeaders [("x-real-ip", id), ("x-forwarded-for", firstIpInXFF)]
+getSource =
+    getSourceFromHeaders
+        [("x-real-ip", firstIpInXFF), ("x-forwarded-for", firstIpInXFF)]
 
 -- | Pull out the first IP in a comma-separated list of X-Forwarded-For IPs.
+--   Leading white spaces are skipped and the IP ends at a white space.
 --
 -- >>> firstIpInXFF "1.2.3.4, 5.6.7.8, 10.11.12.13"
 -- "1.2.3.4"
+-- >>> firstIpInXFF " 1.2.3.4 , 5.6.7.8"
+-- "1.2.3.4"
 --
--- If there are no commas, just return the whole input ByteString:
+-- If there are no commas or white spaces, just return the whole input ByteString:
 --
 -- >>> firstIpInXFF "5.6.7.8"
 -- "5.6.7.8"
@@ -231,9 +319,10 @@
 -- >>> firstIpInXFF "hello, world"
 -- "hello"
 firstIpInXFF :: ByteString -> ByteString
-firstIpInXFF = BS.takeWhile (/= ',')
+firstIpInXFF = BS.takeWhile (\c -> c /= ',' && not (isSpace c)) . BS.dropWhile isSpace
 
-getSourceFromHeaders :: [(HeaderName, ByteString -> ByteString)] -> Request -> Maybe ByteString
+getSourceFromHeaders
+    :: [(HeaderName, ByteString -> ByteString)] -> Request -> Maybe ByteString
 getSourceFromHeaders headerNamesAndPostProc req = getFirst $ foldMap f $ requestHeaders req
   where
     -- Take a header name and value from the request, and try match it against
@@ -242,8 +331,11 @@
     -- to the header value.
     f :: (HeaderName, ByteString) -> First ByteString
     f (headerNameFromReq, headerValFromReq) =
-      let maybePostProc = find (\(headerNameFromPostProc, _) -> headerNameFromReq == headerNameFromPostProc) headerNamesAndPostProc
-      in First $ fmap (\(_, postProc) -> postProc headerValFromReq) maybePostProc
+        let maybePostProc =
+                find
+                    (\(headerNameFromPostProc, _) -> headerNameFromReq == headerNameFromPostProc)
+                    headerNamesAndPostProc
+         in First $ fmap (\(_, postProc) -> postProc headerValFromReq) maybePostProc
 
 -- |
 -- >>> getSourceFromHeaderCustom ["x-foobar"] defaultRequest { requestHeaders = [ ("X-catdog", "1.2.3.4"), ("X-Foobar", "5.6.7.8"), ("Other", "1.1.1.1") ] }
diff --git a/Network/Wai/Logger/IORef.hs b/Network/Wai/Logger/IORef.hs
--- a/Network/Wai/Logger/IORef.hs
+++ b/Network/Wai/Logger/IORef.hs
@@ -1,12 +1,12 @@
 {-# LANGUAGE CPP #-}
 
 module Network.Wai.Logger.IORef (
-       IORef
-     , newIORef
-     , readIORef
-     , writeIORef
-     , atomicModifyIORef'
-     ) where
+    IORef,
+    newIORef,
+    readIORef,
+    writeIORef,
+    atomicModifyIORef',
+) where
 
 import Data.IORef
 
diff --git a/Network/Wai/Logger/IP.hs b/Network/Wai/Logger/IP.hs
--- a/Network/Wai/Logger/IP.hs
+++ b/Network/Wai/Logger/IP.hs
@@ -1,11 +1,12 @@
 module Network.Wai.Logger.IP (
-    NumericAddress, showSockAddr
-  ) where
+    NumericAddress,
+    showSockAddr,
+) where
 
 import Data.Bits (shift, (.&.))
 import Data.Word (Word32)
-import Network.Socket (SockAddr(..))
-import System.ByteOrder (ByteOrder(..), byteOrder)
+import Network.Socket (SockAddr (..))
+import System.ByteOrder (ByteOrder (..), byteOrder)
 import Text.Printf (printf)
 
 -- |  A type for IP address in numeric string representation.
@@ -13,7 +14,7 @@
 
 showIPv4 :: Word32 -> Bool -> NumericAddress
 showIPv4 w32 little
-    | little    = show b1 ++ "." ++ show b2 ++ "." ++ show b3 ++ "." ++ show b4
+    | little = show b1 ++ "." ++ show b2 ++ "." ++ show b3 ++ "." ++ show b4
     | otherwise = show b4 ++ "." ++ show b3 ++ "." ++ show b2 ++ "." ++ show b1
   where
     t1 = w32
@@ -25,25 +26,26 @@
     b3 = t3 .&. 0x000000ff
     b4 = t4 .&. 0x000000ff
 
-showIPv6 :: (Word32,Word32,Word32,Word32) -> String
-showIPv6 (w1,w2,w3,w4) =
+showIPv6 :: (Word32, Word32, Word32, Word32) -> String
+showIPv6 (w1, w2, w3, w4) =
     printf "%x:%x:%x:%x:%x:%x:%x:%x" s1 s2 s3 s4 s5 s6 s7 s8
   where
-    (s1,s2) = split16 w1
-    (s3,s4) = split16 w2
-    (s5,s6) = split16 w3
-    (s7,s8) = split16 w4
-    split16 w = (h1,h2)
+    (s1, s2) = split16 w1
+    (s3, s4) = split16 w2
+    (s5, s6) = split16 w3
+    (s7, s8) = split16 w4
+    split16 w = (h1, h2)
       where
         h1 = shift w (-16) .&. 0x0000ffff
         h2 = w .&. 0x0000ffff
+
 -- | Convert 'SockAddr' to 'NumericAddress'. If the address is
 --   IPv4-embedded IPv6 address, the IPv4 is extracted.
 showSockAddr :: SockAddr -> NumericAddress
 -- HostAddr is network byte order.
-showSockAddr (SockAddrInet _ addr4)                       = showIPv4 addr4 (byteOrder == LittleEndian)
+showSockAddr (SockAddrInet _ addr4) = showIPv4 addr4 (byteOrder == LittleEndian)
 -- HostAddr6 is host byte order.
-showSockAddr (SockAddrInet6 _ _ (0,0,0x0000ffff,addr4) _) = showIPv4 addr4 False
-showSockAddr (SockAddrInet6 _ _ (0,0,0,1) _)              = "::1"
-showSockAddr (SockAddrInet6 _ _ addr6 _)                  = showIPv6 addr6
-showSockAddr (SockAddrUnix _)                             = "-"
+showSockAddr (SockAddrInet6 _ _ (0, 0, 0x0000ffff, addr4) _) = showIPv4 addr4 False
+showSockAddr (SockAddrInet6 _ _ (0, 0, 0, 1) _) = "::1"
+showSockAddr (SockAddrInet6 _ _ addr6 _) = showIPv6 addr6
+showSockAddr (SockAddrUnix _) = "-"
diff --git a/Setup.hs b/Setup.hs
--- a/Setup.hs
+++ b/Setup.hs
@@ -1,4 +1,5 @@
 {-# OPTIONS_GHC -Wall #-}
+
 module Main (main) where
 
 import Distribution.Simple
diff --git a/test/ApacheSpec.hs b/test/ApacheSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/ApacheSpec.hs
@@ -0,0 +1,43 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module ApacheSpec (spec) where
+
+import qualified Data.ByteString.Char8 as BS
+import Data.IORef
+import Network.HTTP.Types (status200)
+import Network.Wai
+import Network.Wai.Logger
+import System.Log.FastLogger
+
+import Test.Hspec
+
+spec :: Spec
+spec = describe "apacheLogger" $ do
+    it "escapes request-derived fields" $ do
+        let req =
+                defaultRequest
+                    { rawPathInfo = "/a\"b"
+                    , requestHeaders = [("X-Forwarded-For", " 1.2.3.4 \"x\"\n, 5.6.7.8")]
+                    , requestHeaderUserAgent = Just "evil\" \"injected\r\nfoo\\"
+                    , requestHeaderReferer = Just "\x01\x7f"
+                    }
+        logLine FromHeader req
+            `shouldReturn` "1.2.3.4 - - [date] \"GET /a\\\"b HTTP/1.0\" 200 4 \"\\x01\\x7f\" \"evil\\\" \\\"injected\\r\\nfoo\\\\\"\n"
+    it "does not change ordinary fields" $ do
+        let req =
+                defaultRequest
+                    { rawPathInfo = "/index.html"
+                    , rawQueryString = "?q=1"
+                    , requestHeaders = [("X-Real-IP", "9.8.7.6")]
+                    , requestHeaderUserAgent = Just "Mozilla/5.0 (X11)"
+                    }
+        logLine FromHeader req
+            `shouldReturn` "9.8.7.6 - - [date] \"GET /index.html?q=1 HTTP/1.0\" 200 4 \"\" \"Mozilla/5.0 (X11)\"\n"
+
+logLine :: IPAddrSource -> Request -> IO BS.ByteString
+logLine ipsrc req = do
+    ref <- newIORef ""
+    let cb s = modifyIORef ref (<> fromLogStr s)
+    lgr <- initLogger ipsrc (LogCallback cb (return ())) (return "date")
+    apacheLogger lgr req status200 (Just 4)
+    readIORef ref
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}
diff --git a/wai-logger.cabal b/wai-logger.cabal
--- a/wai-logger.cabal
+++ b/wai-logger.cabal
@@ -1,6 +1,6 @@
 cabal-version: >=1.10
 name:          wai-logger
-version:       2.5.0
+version:       2.5.1
 license:       BSD3
 license-file:  LICENSE
 maintainer:    Kazu Yamamoto <kazu@iij.ad.jp>
@@ -12,6 +12,7 @@
 description:   A logging system for WAI(Web Application Interface)
 category:      Web, Yesod
 build-type:    Simple
+extra-source-files: ChangeLog.md
 
 source-repository head
     type:     git
@@ -37,3 +38,20 @@
 
     if impl(ghc >=8)
         default-extensions: Strict StrictData
+
+test-suite spec
+    type:             exitcode-stdio-1.0
+    main-is:          Spec.hs
+    build-tools:      hspec-discover >=2.6
+    hs-source-dirs:   test
+    other-modules:    ApacheSpec
+    default-language: Haskell2010
+    ghc-options:      -Wall
+    build-depends:
+        base >=4 && <5,
+        bytestring,
+        fast-logger,
+        hspec,
+        http-types,
+        wai,
+        wai-logger
