diff --git a/System/Log/FastLogger.hs b/System/Log/FastLogger.hs
--- a/System/Log/FastLogger.hs
+++ b/System/Log/FastLogger.hs
@@ -53,13 +53,14 @@
 -- | Creating a new 'LoggerSet'.
 --   If 'Nothing' is specified to the second argument,
 --   stdout is used.
+--   Please note that the minimum 'BufSize' is 1.
 newLoggerSet :: BufSize -> Maybe FilePath -> IO LoggerSet
 newLoggerSet size mfile = do
     fd <- case mfile of
         Nothing   -> return stdout
         Just file -> logOpen file
     n <- getNumCapabilities
-    loggers <- replicateM n $ newLogger size
+    loggers <- replicateM n $ newLogger (max 1 size)
     let arr = listArray (0,n-1) loggers
     fref <- newIORef fd
     return $ LoggerSet mfile fref arr
diff --git a/System/Log/FastLogger/Logger.hs b/System/Log/FastLogger/Logger.hs
--- a/System/Log/FastLogger/Logger.hs
+++ b/System/Log/FastLogger/Logger.hs
@@ -34,7 +34,7 @@
 pushLog fd logger@(Logger mbuf size ref) nlogmsg@(LogStr nlen nbuilder)
   | nlen > size = do
       flushLog fd logger
-      withMVar mbuf $ \buf -> toBufIOWith buf nlen (write fd) nbuilder
+      withMVar mbuf $ \buf -> toBufIOWith buf size (write fd) nbuilder
   | otherwise = do
     mmsg <- atomicModifyIORef' ref checkBuf
     case mmsg of
diff --git a/fast-logger.cabal b/fast-logger.cabal
--- a/fast-logger.cabal
+++ b/fast-logger.cabal
@@ -1,5 +1,5 @@
 Name:                   fast-logger
-Version:                2.1.1
+Version:                2.1.2
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3