diff --git a/Crypto/KDF/PBKDF2.hs b/Crypto/KDF/PBKDF2.hs
index 7a3337c..027086e 100644
--- a/Crypto/KDF/PBKDF2.hs
+++ b/Crypto/KDF/PBKDF2.hs
@@ -54,7 +54,7 @@ data Parameters = Parameters
     }
 
 -- | generate the pbkdf2 key derivation function from the output
-generate :: (ByteArrayAccess salt, ByteArray ba)
+generate :: (ByteArrayAccess password, ByteArrayAccess salt, ByteArray ba)
          => PRF password
          -> Parameters
          -> password
diff --git a/Crypto/Number/Serialize.hs b/Crypto/Number/Serialize.hs
index 9855c5b..858e848 100644
--- a/Crypto/Number/Serialize.hs
+++ b/Crypto/Number/Serialize.hs
@@ -35,6 +35,7 @@ i2osp m = B.allocAndFreeze sz (\p -> Internal.i2osp m p sz >> return ())
 -- | Just like 'i2osp', but takes an extra parameter for size.
 -- If the number is too big to fit in @len@ bytes, 'Nothing' is returned
 -- otherwise the number is padded with 0 to fit the @len@ required.
+{-# INLINABLE i2ospOf #-}
 i2ospOf :: B.ByteArray ba => Int -> Integer -> Maybe ba
 i2ospOf len m
     | len <= 0  = Nothing
diff --git a/Crypto/OTP.hs b/Crypto/OTP.hs
index 9b5b383..44503ff 100644
--- a/Crypto/OTP.hs
+++ b/Crypto/OTP.hs
@@ -129,8 +129,8 @@ defaultTOTPParams :: TOTPParams SHA1
 defaultTOTPParams = TP SHA1 0 30 OTP6 TwoSteps
 
 -- | Create a TOTP configuration with customized parameters.
-mkTOTPParams ::
-    hash
+mkTOTPParams :: (HashAlgorithm hash)
+    => hash
     -> OTPTime
     -- ^ The T0 parameter in seconds. This is the Unix time from which to start
     -- counting steps (default 0). Must be before the current time.
diff --git a/Crypto/Random/Types.hs b/Crypto/Random/Types.hs
index 2806fc3..961be8a 100644
--- a/Crypto/Random/Types.hs
+++ b/Crypto/Random/Types.hs
@@ -56,5 +56,5 @@ instance DRG gen => MonadRandom (MonadPseudoRandom gen) where
 
 -- | Run a pure computation with a Deterministic Random Generator
 -- in the 'MonadPseudoRandom'
-withDRG :: gen -> MonadPseudoRandom gen a -> (a, gen)
+withDRG :: DRG gen => gen -> MonadPseudoRandom gen a -> (a, gen)
 withDRG gen m = runPseudoRandom m gen
diff --git a/tests/BlockCipher.hs b/tests/BlockCipher.hs
index 38adcb2..2fc1248 100644
--- a/tests/BlockCipher.hs
+++ b/tests/BlockCipher.hs
@@ -307,7 +307,7 @@ generateIvAEAD :: Gen B.ByteString
 generateIvAEAD = choose (12,90) >>= \sz -> (B.pack <$> replicateM sz arbitrary)
 
 -- | Generate a plaintext multiple of blocksize bytes
-generatePlaintextMultipleBS :: Gen (PlaintextBS a)
+generatePlaintextMultipleBS :: BlockCipher a => Gen (PlaintextBS a)
 generatePlaintextMultipleBS = choose (1,128) >>= \size -> replicateM (size * 16) arbitrary >>= return . PlaintextBS . B.pack
 
 -- | Generate any sized plaintext
@@ -474,7 +474,7 @@ testBlockCipher kats cipher = testGroup (cipherName cipher)
     ++ testModes cipher ++ testIvArith cipher
     )
 
-cipherMakeKey :: cipher -> ByteString -> Key cipher
+cipherMakeKey :: Cipher cipher => cipher -> ByteString -> Key cipher
 cipherMakeKey _ bs = Key bs
 
 cipherMakeIV :: BlockCipher cipher => cipher -> ByteString -> IV cipher