diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -101,8 +101,8 @@
 lexByteString :: ByteString.ByteString -> Maybe [ByteString.ByteString]
 lexByteString s0 = go s0 id where
     go s acc = case runInputByteString (tlexScan ()) s of
-        (TlexEndOfInput, _)            -> Just $ acc []
-        (TlexError, _)                 -> Nothing
+        (TlexEndOfInput, _)     -> Just $ acc []
+        (TlexNotAccepted, _)    -> Nothing
         (TlexAccepted n act, _) ->
             let (consumed, rest) = splitAt n s
                 token = act consumed
diff --git a/src/Language/Lexer/Tlex/Runner.hs b/src/Language/Lexer/Tlex/Runner.hs
--- a/src/Language/Lexer/Tlex/Runner.hs
+++ b/src/Language/Lexer/Tlex/Runner.hs
@@ -18,7 +18,7 @@
 data TlexResult mark action
     = TlexEndOfInput
     -- ^ No more inputs.
-    | TlexError
+    | TlexNotAccepted
     -- ^ Some inputs are available, but not accepted.
     | TlexAccepted mark action
     -- ^ Accepted with a end position and an action.
@@ -72,5 +72,5 @@
             pure do TlexAccepted m x
 
         goEnd preAccepted = case preAccepted of
-            Nothing  -> pure TlexError
+            Nothing  -> pure TlexNotAccepted
             Just acc -> pure acc
diff --git a/tlex.cabal b/tlex.cabal
--- a/tlex.cabal
+++ b/tlex.cabal
@@ -2,7 +2,7 @@
 build-type:          Custom
 
 name:                tlex
-version:             0.4.0.1
+version:             0.5.0.0
 license:             Apache-2.0 OR MPL-2.0
 license-file:        LICENSE
 copyright:           (c) 2020 Mizunashi Mana