diff --git a/src/C/Zcash.chs b/src/C/Zcash.chs
index f0ad1b8..fcabf7c 100644
--- a/src/C/Zcash.chs
+++ b/src/C/Zcash.chs
@@ -128,8 +128,8 @@ import ZcashHaskell.Types
 
 {# fun unsafe rust_wrapper_sapling_spendingkey as rustWrapperSaplingSpendingkey
      { toBorshVar* `BS.ByteString'&
-     , `Int'
-     , `Int'
+     , `Word32'
+     , `Word32'
      , getVarBuffer `Buffer (BS.ByteString)'&
      }
   -> `()'
diff --git a/src/ZcashHaskell/Sapling.hs b/src/ZcashHaskell/Sapling.hs
index 81d6507..d32668e 100644
--- a/src/ZcashHaskell/Sapling.hs
+++ b/src/ZcashHaskell/Sapling.hs
@@ -90,7 +90,7 @@ instance FromJSON RawTxResponse where
           pure $ RawTxResponse i h (getShieldedOutputs h) a ht c b
 
 -- | Attempts to obtain a sapling SpendinKey using a HDSeed, a Coin Type and an Account ID
-genSaplingSpendingKey :: BS.ByteString -> Int -> Int -> Maybe BS.ByteString
+genSaplingSpendingKey :: BS.ByteString -> Word32 -> Word32 -> Maybe BS.ByteString
 genSaplingSpendingKey seed coin_type account_id = do
   if BS.length res > 0
     then Just res
diff --git a/test/Spec.hs b/test/Spec.hs
index c9ceab8..8032b6d 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -62,6 +62,10 @@ import Foreign.C.Types
 import Data.Word
 import Haskoin.Crypto.Keys.Extended
 
+m2bs :: Maybe BS.ByteString -> BS.ByteString 
+m2bs x = fromMaybe "" x 
+
+
 main :: IO ()
 main = do
   hspec $ do
@@ -512,5 +516,8 @@ main = do
                   ] :: [Word8]
           let coin  = 1 :: Word32
           let account = 0 :: Word32
-          res <- genSaplingSpendingKey (word8ArrayToByteString hdseed) coin account
-          res `shouldBe` "genSaplingSpendingKey Function called."
\ No newline at end of file
+          let msg = genSaplingSpendingKey (word8ArrayToByteString hdseed) coin account
+          case msg of
+              Nothing -> "Bad response from genSapingSpendingKey"
+              Just msg -> fromMaybe "BadResponse" msg
+          "mm " `shouldBe` "genSaplingSpendingKey Function called."
\ No newline at end of file