diff --git a/bench/main.hs b/bench/main.hs
--- a/bench/main.hs
+++ b/bench/main.hs
@@ -15,7 +15,7 @@
 
 import qualified Data.ByteString.Read as R
 import qualified Data.Text.Read as T
-import qualified Data.ByteString.Lex.Double as Lex
+import qualified Data.ByteString.Lex.Fractional as Lex
 import qualified Data.Attoparsec.ByteString.Char8 as A
 
 short :: IsString s => s
@@ -38,7 +38,7 @@
 text = either (const $ error "parse error") checkConsumed . T.signed T.double . T.decodeUtf8
 
 bytestringLexing :: ByteString -> Double
-bytestringLexing = maybe (error "parse error") checkConsumed . Lex.readDouble
+bytestringLexing = maybe (error "parse error") checkConsumed . Lex.readSigned Lex.readExponential
 
 attoparsec :: ByteString -> Double
 attoparsec = either (const $ error "parse error") id . A.parseOnly (fmap toRealFloat A.scientific)
diff --git a/bytestring-read.cabal b/bytestring-read.cabal
--- a/bytestring-read.cabal
+++ b/bytestring-read.cabal
@@ -1,5 +1,5 @@
 name:                bytestring-read
-version:             0.3.0
+version:             0.3.1
 synopsis:            fast ByteString to number converting library
 description:         benchmark: <http://philopon.github.io/bytestring-read/bench.html>
 license:             MIT
@@ -33,8 +33,8 @@
                      , bytestring-read
                      , bytestring
                      , text
-                     , bytestring-lexing >=0.4  && <0.5
-                     , criterion         >=1.0  && <1.2
+                     , bytestring-lexing >=0.5  && <0.6
+                     , criterion         >=0.8  && <1.2
                      , scientific
                      , attoparsec
   ghc-options:         -Wall -O2
diff --git a/src/Data/ByteString/Read/Class.hs b/src/Data/ByteString/Read/Class.hs
--- a/src/Data/ByteString/Read/Class.hs
+++ b/src/Data/ByteString/Read/Class.hs
@@ -93,11 +93,11 @@
     {-# INLINE isDigit #-};\
     {-# INLINE unsafeToDigit #-};\
     isDigit _ = \w -> 48 <= w && w <= 57 || 65 <= w && w <= MAXu || 97 <= w && w <= MAXl;\
-    unsafeToDigit _ w = if 48 <= w && w <= 57;\
-                        then fromIntegral w - 48;\
-                        else if 65 <= w && w <= 90;\
-                             then fromIntegral w - 55;\
-                             else fromIntegral w - 87
+    unsafeToDigit _ w = if w <= 57;\
+                        then w - 48;\
+                        else if w <= 90;\
+                             then w - 55;\
+                             else w - 87
 
 defineRadixOver10(11, 65, 97)
 defineRadixOver10(12, 66, 98)