diff --git a/src/Data/ByteString/Lazy/ToolsYj.hs b/src/Data/ByteString/Lazy/ToolsYj.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/ByteString/Lazy/ToolsYj.hs
@@ -0,0 +1,13 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
+
+module Data.ByteString.Lazy.ToolsYj (
+	splitAt' ) where
+
+import Data.Int
+import Data.ByteString.Lazy qualified as LBS
+
+splitAt' :: Int64 -> LBS.ByteString -> Maybe (LBS.ByteString, LBS.ByteString)
+splitAt' n bs
+	| LBS.length bs < n = Nothing
+	| otherwise = Just $ LBS.splitAt n bs
diff --git a/tools-yj.cabal b/tools-yj.cabal
--- a/tools-yj.cabal
+++ b/tools-yj.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           tools-yj
-version:        0.1.0.29
+version:        0.1.0.30
 synopsis:       Tribial tools
 description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/tools-yj#readme>
 category:       Tools
@@ -31,6 +31,7 @@
       Control.Monad.ToolsYj
       Data.Bits.ToolsYj
       Data.Bool.ToolsYj
+      Data.ByteString.Lazy.ToolsYj
       Data.ByteString.ToolsYj
       Data.Either.ToolsYj
       Data.Function.ToolsYj