diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,13 @@
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## 0.2.2
+### Removed
+- Hide tweak negation behind a flag for compatibilidy with Debian 9.
+
+### Fixed
+- Correct code that was not compiling with some flags enabled.
+
 ## 0.2.1
 ### Changed
 - Do not depend on hardcoded DER signatures in tests.
diff --git a/secp256k1-haskell.cabal b/secp256k1-haskell.cabal
--- a/secp256k1-haskell.cabal
+++ b/secp256k1-haskell.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: aaa369b9f2d9817845daa3c657860285c04c9ef6c6d22ec3c4b566821e7b8f5d
+-- hash: 0b75b1185f390c0f03f09dfc8e18349a5bce92770b10888fc121279d4fa9953f
 
 name:           secp256k1-haskell
-version:        0.2.1
+version:        0.2.2
 synopsis:       Bindings for secp256k1 library from Bitcoin Core
 description:    Sign and verify signatures using the very fast C secp256k1 library from Pieter Wuille. Has Haskell types and abstractions for keys and signatures.
 category:       Crypto
@@ -32,6 +32,11 @@
   manual: True
   default: False
 
+flag negate
+  description: Enable tweak negate
+  manual: True
+  default: False
+
 flag recovery
   description: Enable signature key recovery APIs
   manual: True
@@ -68,6 +73,8 @@
     cpp-options: -DSCHNORR
   if flag(recovery)
     cpp-options: -DRECOVERY
+  if flag(negate)
+    cpp-options: -DNEGATE
   default-language: Haskell2010
 
 test-suite spec
diff --git a/src/Crypto/Secp256k1.hs b/src/Crypto/Secp256k1.hs
--- a/src/Crypto/Secp256k1.hs
+++ b/src/Crypto/Secp256k1.hs
@@ -59,7 +59,9 @@
     , tweakAddPubKey
     , tweakMulPubKey
     , combinePubKeys
+#ifdef NEGATE
     , tweakNegate
+#endif
 
 #ifdef ECDH
     -- * Diffie Hellman
@@ -89,12 +91,15 @@
 import           Data.ByteString.Short     (fromShort, toShort)
 import           Data.Hashable             (Hashable (..))
 import           Data.Maybe                (fromJust, fromMaybe, isJust)
+import           Data.Serialize            (decode, encode)
 import           Data.String               (IsString (..))
 import           Data.String.Conversions   (ConvertibleStrings, cs)
-import           Foreign                   (ForeignPtr, alloca, allocaArray,
-                                            allocaBytes, mallocForeignPtr,
+import           Foreign                   (ForeignPtr, alloca,
+                                            allocaArray, allocaBytes,
+                                            mallocForeignPtr, 
                                             nullPtr, peek, poke, pokeArray,
                                             withForeignPtr)
+import           Foreign.C.Types           (CInt)
 import           System.IO.Unsafe          (unsafePerformIO)
 import           Test.QuickCheck           (Arbitrary (..),
                                             arbitraryBoundedRandom, suchThat)
@@ -482,15 +487,18 @@
 
 -- | Add multiple public keys together.
 combinePubKeys :: [PubKey] -> Maybe PubKey
-combinePubKeys pubs = withContext $ \ctx -> pointers [] pubs $ \ps ->
-    allocaArray (length ps) $ \a -> do
-        pokeArray a ps
-        fp <- mallocForeignPtr
-        ret <- withForeignPtr fp $ \p ->
-            ecPubKeyCombine ctx p a (fromIntegral $ length ps)
-        if isSuccess ret
-            then return $ Just $ PubKey fp
-            else return Nothing
+combinePubKeys pubs = withContext $ \ctx ->
+    if pubs == []
+        then return Nothing
+        else pointers [] pubs $ \ps ->
+            allocaArray (length ps) $ \a -> do
+                pokeArray a ps
+                fp <- mallocForeignPtr
+                ret <- withForeignPtr fp $ \p ->
+                    ecPubKeyCombine ctx p a (fromIntegral $ length ps)
+                if isSuccess ret
+                    then return $ Just $ PubKey fp
+                    else return Nothing
   where
     pointers ps [] f = f ps
     pointers ps (PubKey fp : pubs') f =
@@ -539,7 +547,7 @@
     withForeignPtr fk $ \k -> withForeignPtr fm $ \m -> do
         fg <- mallocForeignPtr
         ret <- withForeignPtr fg $ \g ->
-            ecdsaSignRecoverable ctx g m k nullFunPtr nullPtr
+            ecdsaSignRecoverable ctx g m k nullPtr nullPtr
         unless (isSuccess ret) $ error "could not sign message"
         return $ RecSig fg
 
@@ -552,6 +560,7 @@
         if isSuccess ret then return $ Just $ PubKey fp else return Nothing
 #endif
 
+#ifdef NEGATE
 tweakNegate :: Tweak -> Maybe Tweak
 tweakNegate (Tweak fk) = withContext $ \ctx -> do
     fnew <- mallocForeignPtr
@@ -563,6 +572,7 @@
         if isSuccess ret
             then Just (Tweak fnew)
             else Nothing
+#endif
 
 #ifdef ECDH
 -- | Compute Diffie-Hellman secret.
@@ -608,10 +618,14 @@
         if isSuccess ret then return $ Just $ SecKey fk' else return Nothing
 
 signMsgSchnorr :: SecKey -> Msg -> SchnorrSig
-signMsgSchnorr (SecKey fk) (Msg fm) = withContext $ \ctx ->
-    withForeignPtr fk $ \k -> withForeignPtr fm $ \m -> do
+signMsgSchnorr (SecKey fk) (Msg fm) =
+  withContext $ \ctx ->
+    withForeignPtr fk $ \k ->
+      withForeignPtr fm $ \m -> do
         fg <- mallocForeignPtr
-        ret <- withForeignPtr fg $ \g -> schnorrSign ctx g m k nullFunPtr nullPtr
+        ret <-
+          withForeignPtr fg $ \g ->
+            schnorrSign ctx g m k nullPtr nullPtr
         unless (isSuccess ret) $ error "could not schnorr-sign message"
         return $ SchnorrSig fg
 
diff --git a/src/Crypto/Secp256k1/Internal.hs b/src/Crypto/Secp256k1/Internal.hs
--- a/src/Crypto/Secp256k1/Internal.hs
+++ b/src/Crypto/Secp256k1/Internal.hs
@@ -23,6 +23,7 @@
 import qualified Data.Serialize.Get    as Get
 import qualified Data.Serialize.Put    as Put
 import           Data.Void             (Void)
+import           Data.Word             (Word8)
 import           Foreign               (ForeignPtr, FunPtr, Ptr, Storable (..),
                                         alloca, castPtr, copyArray,
                                         newForeignPtr, withForeignPtr)
@@ -413,12 +414,14 @@
     -> Ptr Tweak32
     -> IO Ret
 
+#ifdef NEGATE
 foreign import ccall
     "secp256k1.h secp256k1_ec_privkey_negate"
     ecTweakNegate
     :: Ptr Ctx
     -> Ptr Tweak32
     -> IO Ret
+#endif
 
 foreign import ccall
     "secp256k1.h secp256k1_ec_pubkey_tweak_add"
diff --git a/test/Crypto/Secp256k1Spec.hs b/test/Crypto/Secp256k1Spec.hs
--- a/test/Crypto/Secp256k1Spec.hs
+++ b/test/Crypto/Secp256k1Spec.hs
@@ -6,12 +6,11 @@
 import qualified Data.ByteString.Base16  as B16
 import qualified Data.ByteString.Char8   as B8
 import           Data.Maybe              (fromMaybe)
-import           Data.Serialize
 import           Data.String             (fromString)
 import           Data.String.Conversions (cs)
 import           Test.Hspec
 import           Test.HUnit              (Assertion, assertEqual)
-import           Test.QuickCheck         (Property, property, (==>))
+import           Test.QuickCheck         (property)
 
 spec :: Spec
 spec = do
@@ -57,7 +56,10 @@
         it "add public key" $ property $ tweakAddPubKeyTest
         it "multiply public key" $ property $ tweakMulPubKeyTest
         it "combine public keys" $ property $ combinePubKeyTest
+        it "can't combine 0 public keys" $ property $ combinePubKeyEmptyListTest
+#ifdef NEGATE
         it "negates tweak" $ property $ negateTweakTest
+#endif
 #ifdef ECDH
     describe "ecdh" $ do
         it "computes dh secret" $ property $ computeDhSecret
@@ -277,6 +279,14 @@
     expected = importPubKey $ hexToBytes
         "043d9a7ec70011efc23c33a7e62d2ea73cca87797e3b659d93bea6aa871aebde56c3bc6134ca82e324b0ab9c0e601a6d2933afe7fb5d9f3aae900f5c5dc6e362c8"
 
+combinePubKeyEmptyListTest :: Assertion
+combinePubKeyEmptyListTest =
+    assertEqual "empty pubkey list must return Nothing" expected combined
+  where
+    expected = Nothing
+    combined = combinePubKeys []
+
+#ifdef NEGATE
 negateTweakTest :: Assertion
 negateTweakTest =
     assertEqual "can recover secret key 1 after adding tweak 1" oneKey subtracted
@@ -288,6 +298,7 @@
     Just minusOneTwk = tweakNegate oneTwk
     Just twoKey = tweakAddSecKey oneKey oneTwk
     Just subtracted = tweakAddSecKey twoKey minusOneTwk
+#endif
 
 #ifdef ECDH
 computeDhSecret :: Assertion