diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,10 @@
 <!-- -*- Markdown -*- -->
 
+## 0.6.7.1
+
+- fix do safe convert for integral conversion from SQL value.
+- add test suite of conversion from and to SQL value.
+
 ## 0.6.7.0
 
 - add bulkInsert definitions, and deprecate chunksInsert.
diff --git a/relational-query-HDBC.cabal b/relational-query-HDBC.cabal
--- a/relational-query-HDBC.cabal
+++ b/relational-query-HDBC.cabal
@@ -1,5 +1,5 @@
 name:                relational-query-HDBC
-version:             0.6.7.0
+version:             0.6.7.1
 synopsis:            HDBC instance of relational-query and typed query interface for HDBC
 description:         This package contains the HDBC instance of relational-query and
                      the typed query interface for HDBC.
@@ -72,6 +72,18 @@
 
   default-language:    Haskell2010
 
+test-suite convertible-iso
+  build-depends:         base <5
+                       , QuickCheck
+                       , quickcheck-simple
+                       , convertible
+                       , HDBC
+                       , relational-query-HDBC
+  type:                exitcode-stdio-1.0
+  main-is:             convertibleIso.hs
+  hs-source-dirs:      test
+  ghc-options:         -Wall
+  default-language:    Haskell2010
 
 source-repository head
   type:       git
diff --git a/src/Database/HDBC/SqlValueExtra.hs b/src/Database/HDBC/SqlValueExtra.hs
--- a/src/Database/HDBC/SqlValueExtra.hs
+++ b/src/Database/HDBC/SqlValueExtra.hs
@@ -1,9 +1,10 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleContexts #-}
 {-# OPTIONS -fno-warn-orphans #-}
 
 -- |
 -- Module      : Database.HDBC.SqlValueExtra
--- Copyright   : 2013 Kei Hibino
+-- Copyright   : 2013-2018 Kei Hibino
 -- License     : BSD3
 --
 -- Maintainer  : ex8k.hibino@gmail.com
@@ -20,9 +21,9 @@
 safeConvertFromIntegral32 i =
   safeConvert (fromIntegral i :: Int32)
 
-safeConvertToIntegral32 :: Integral a => SqlValue -> ConvertResult a
+safeConvertToIntegral32 :: Convertible Int32 a => SqlValue -> ConvertResult a
 safeConvertToIntegral32 v =
-  fmap fromIntegral (safeConvert v :: ConvertResult Int32)
+  safeConvert =<< (safeConvert v :: ConvertResult Int32)
 
 instance Convertible Int8 SqlValue where
   safeConvert = safeConvertFromIntegral32
diff --git a/test/convertibleIso.hs b/test/convertibleIso.hs
new file mode 100644
--- /dev/null
+++ b/test/convertibleIso.hs
@@ -0,0 +1,64 @@
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE FlexibleContexts #-}
+
+import Control.Applicative ((<$>))
+import Data.Int (Int8, Int16)
+import Data.Convertible (Convertible, safeConvert, ConvertResult)
+import Database.HDBC (SqlValue (SqlInteger))
+
+import Test.QuickCheck (Arbitrary (..), resize)
+import Test.QuickCheck.Simple (qcTest, defaultMain)
+
+import Database.HDBC.Record.Persistable ()
+
+
+
+prop_toFromQvInt8 :: Int8 -> Bool
+prop_toFromQvInt8 i8 = Right i8 == (safeConvert =<< sv)
+  where
+    sv :: ConvertResult SqlValue
+    sv = safeConvert i8
+
+prop_toFromQvInt16 :: Int16 -> Bool
+prop_toFromQvInt16 i16 = Right i16 == (safeConvert =<< sv)
+  where
+    sv :: ConvertResult SqlValue
+    sv = safeConvert i16
+
+
+newtype IntegerR i =
+  IntegerR Integer
+  deriving (Eq, Show)
+
+instance Arbitrary (IntegerR Int8) where
+  arbitrary = IntegerR <$> resize 1000 arbitrary
+
+instance Arbitrary (IntegerR Int16) where
+  arbitrary = IntegerR <$> resize 100000 arbitrary
+
+
+prop_fromToQvBounded :: (Integral a, Convertible SqlValue a, Convertible a SqlValue)
+                     => a -> a -> IntegerR a -> Bool
+prop_fromToQvBounded mn' mx' (IntegerR i)
+  | i < mn || mx < i  =  True
+  | otherwise         =  Right sv == (safeConvert =<< ix)
+  where
+    sv = SqlInteger i
+    ix = safeConvert sv `asTypeOf` Right mn'
+    mn = fromIntegral mn'
+    mx = fromIntegral mx'
+
+prop_fromToQvInt8 :: IntegerR Int8 -> Bool
+prop_fromToQvInt8 = prop_fromToQvBounded minBound maxBound
+
+prop_fromToQvInt16 :: IntegerR Int16 -> Bool
+prop_fromToQvInt16 = prop_fromToQvBounded minBound maxBound
+
+main :: IO ()
+main =
+  defaultMain
+  [ qcTest "int8  - to SqlV from SqlV" prop_toFromQvInt8
+  , qcTest "int16 - to SqlV from SqlV" prop_toFromQvInt16
+  , qcTest "int8  - from SqlV to SqlV" prop_fromToQvInt8
+  , qcTest "int16 - from SqlV to SqlV" prop_fromToQvInt16
+  ]