diff --git a/CHANGELOG.md b/CHANGELOG.md
index 26c53b7..b967519 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,8 @@
 ## 0.9
 
 * Quiet down unused module imports
+* Move Curve25519 over to Crypto.Error instead of using Either String.
+
 ## 0.8
 
 * Add support for ChaChaPoly1305 Nonce Increment (John Galt)
diff --git a/Crypto/Error/Types.hs b/Crypto/Error/Types.hs
index fa07cb7..3163675 100644
--- a/Crypto/Error/Types.hs
+++ b/Crypto/Error/Types.hs
@@ -33,6 +33,7 @@ data CryptoError =
     | CryptoError_SecretKeySizeInvalid
     | CryptoError_SecretKeyStructureInvalid
     | CryptoError_PublicKeySizeInvalid
+    | CryptoError_SharedSecretSizeInvalid
     -- Message authentification error
     | CryptoError_MacKeyInvalid
     deriving (Show,Eq,Enum,Data,Typeable)
diff --git a/Crypto/PubKey/Curve25519.hs b/Crypto/PubKey/Curve25519.hs
index 4d5863c..32163bd 100644
--- a/Crypto/PubKey/Curve25519.hs
+++ b/Crypto/PubKey/Curve25519.hs
@@ -26,6 +26,7 @@ import           Data.Word
 import           Foreign.Ptr
 import           GHC.Ptr
 
+import           Crypto.Error
 import           Crypto.Internal.Compat
 import           Crypto.Internal.Imports
 import           Crypto.Internal.ByteArray (ByteArrayAccess, ScrubbedBytes, Bytes, withByteArray)
@@ -45,21 +46,21 @@ newtype DhSecret = DhSecret ScrubbedBytes
     deriving (Show,Eq,ByteArrayAccess,NFData)
 
 -- | Try to build a public key from a bytearray
-publicKey :: ByteArrayAccess bs => bs -> Either String PublicKey
+publicKey :: ByteArrayAccess bs => bs -> CryptoFailable PublicKey
 publicKey bs
-    | B.length bs == 32 = Right $ PublicKey $ B.copyAndFreeze bs (\_ -> return ())
-    | otherwise               = Left "invalid public key size"
+    | B.length bs == 32 = CryptoPassed $ PublicKey $ B.copyAndFreeze bs (\_ -> return ())
+    | otherwise         = CryptoFailed CryptoError_PublicKeySizeInvalid
 
 -- | Try to build a secret key from a bytearray
-secretKey :: ByteArrayAccess bs => bs -> Either String SecretKey
+secretKey :: ByteArrayAccess bs => bs -> CryptoFailable SecretKey
 secretKey bs
     | B.length bs == 32 = unsafeDoIO $ do
         withByteArray bs $ \inp -> do
             valid <- isValidPtr inp
             if valid
-                then (Right . SecretKey) <$> B.copy bs (\_ -> return ())
-                else return $ Left "invalid secret key"
-    | otherwise = Left "secret key invalid size"
+                then (CryptoPassed . SecretKey) <$> B.copy bs (\_ -> return ())
+                else return $ CryptoFailed CryptoError_SecretKeyStructureInvalid
+    | otherwise = CryptoFailed CryptoError_SecretKeySizeInvalid
   where
         --  e[0] &= 0xf8;
         --  e[31] &= 0x7f;
@@ -80,10 +81,10 @@ secretKey bs
 {-# NOINLINE secretKey #-}
 
 -- | Create a DhSecret from a bytearray object
-dhSecret :: ByteArrayAccess b => b -> Either String DhSecret
+dhSecret :: ByteArrayAccess b => b -> CryptoFailable DhSecret
 dhSecret bs
-    | B.length bs == 32 = Right $ DhSecret $ B.copyAndFreeze bs (\_ -> return ())
-    | otherwise         = Left "invalid dh secret size"
+    | B.length bs == 32 = CryptoPassed $ DhSecret $ B.copyAndFreeze bs (\_ -> return ())
+    | otherwise         = CryptoFailed CryptoError_SharedSecretSizeInvalid
 
 -- | Compute the Diffie Hellman secret from a public key and a secret key
 dh :: PublicKey -> SecretKey -> DhSecret
diff --git a/tests/KAT_Curve25519.hs b/tests/KAT_Curve25519.hs
index 02a3836..ad368f5 100644
--- a/tests/KAT_Curve25519.hs
+++ b/tests/KAT_Curve25519.hs
@@ -1,14 +1,15 @@
 {-# LANGUAGE OverloadedStrings #-}
 module KAT_Curve25519 ( tests ) where
 
+import           Crypto.Error
 import qualified Crypto.PubKey.Curve25519 as Curve25519
 import           Data.ByteArray as B
 import           Imports
 
-alicePrivate = either error id $ Curve25519.secretKey ("\x77\x07\x6d\x0a\x73\x18\xa5\x7d\x3c\x16\xc1\x72\x51\xb2\x66\x45\xdf\x4c\x2f\x87\xeb\xc0\x99\x2a\xb1\x77\xfb\xa5\x1d\xb9\x2c\x2a" :: ByteString)
-alicePublic  = either error id $ Curve25519.publicKey ("\x85\x20\xf0\x09\x89\x30\xa7\x54\x74\x8b\x7d\xdc\xb4\x3e\xf7\x5a\x0d\xbf\x3a\x0d\x26\x38\x1a\xf4\xeb\xa4\xa9\x8e\xaa\x9b\x4e\x6a" :: ByteString)
-bobPrivate   = either error id $ Curve25519.secretKey ("\x5d\xab\x08\x7e\x62\x4a\x8a\x4b\x79\xe1\x7f\x8b\x83\x80\x0e\xe6\x6f\x3b\xb1\x29\x26\x18\xb6\xfd\x1c\x2f\x8b\x27\xff\x88\xe0\xeb" :: ByteString)
-bobPublic    = either error id $ Curve25519.publicKey ("\xde\x9e\xdb\x7d\x7b\x7d\xc1\xb4\xd3\x5b\x61\xc2\xec\xe4\x35\x37\x3f\x83\x43\xc8\x5b\x78\x67\x4d\xad\xfc\x7e\x14\x6f\x88\x2b\x4f" :: ByteString)
+alicePrivate = throwCryptoError $ Curve25519.secretKey ("\x77\x07\x6d\x0a\x73\x18\xa5\x7d\x3c\x16\xc1\x72\x51\xb2\x66\x45\xdf\x4c\x2f\x87\xeb\xc0\x99\x2a\xb1\x77\xfb\xa5\x1d\xb9\x2c\x2a" :: ByteString)
+alicePublic  = throwCryptoError $ Curve25519.publicKey ("\x85\x20\xf0\x09\x89\x30\xa7\x54\x74\x8b\x7d\xdc\xb4\x3e\xf7\x5a\x0d\xbf\x3a\x0d\x26\x38\x1a\xf4\xeb\xa4\xa9\x8e\xaa\x9b\x4e\x6a" :: ByteString)
+bobPrivate   = throwCryptoError $ Curve25519.secretKey ("\x5d\xab\x08\x7e\x62\x4a\x8a\x4b\x79\xe1\x7f\x8b\x83\x80\x0e\xe6\x6f\x3b\xb1\x29\x26\x18\xb6\xfd\x1c\x2f\x8b\x27\xff\x88\xe0\xeb" :: ByteString)
+bobPublic    = throwCryptoError $ Curve25519.publicKey ("\xde\x9e\xdb\x7d\x7b\x7d\xc1\xb4\xd3\x5b\x61\xc2\xec\xe4\x35\x37\x3f\x83\x43\xc8\x5b\x78\x67\x4d\xad\xfc\x7e\x14\x6f\x88\x2b\x4f" :: ByteString)
 aliceMultBob = "\x4a\x5d\x9d\x5b\xa4\xce\x2d\xe1\x72\x8e\x3b\xf4\x80\x35\x0f\x25\xe0\x7e\x21\xc9\x47\xd1\x9e\x33\x76\xf0\x9b\x3c\x1e\x16\x17\x42" :: ByteString
 
 katTests :: [TestTree]