diff --git a/src/Text/Show/ToolsYj.hs b/src/Text/Show/ToolsYj.hs
--- a/src/Text/Show/ToolsYj.hs
+++ b/src/Text/Show/ToolsYj.hs
@@ -7,7 +7,7 @@
 class ShowIO a where
 	showIO :: a -> IO String
 
-instance Show a => ShowIO a where
+instance {-# OVERLAPPABLE #-} Show a => ShowIO a where
 	showIO = pure . show
 
 printIO :: ShowIO a => a -> IO ()
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:        0.1.0.22
+version:        0.1.0.23
 synopsis:       Tribial tools
 description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/tools-yj#readme>
 category:       Tools