diff --git a/flake.nix b/flake.nix
index c480d7021..75b3b7472 100644
--- a/flake.nix
+++ b/flake.nix
@@ -38,7 +38,7 @@
             }))
             (haskell.lib.compose.addTestToolDepends [ solc z3 cvc5 ])
             (haskell.lib.compose.appendConfigureFlags (
-              [ "--ghc-option=-O2" ]
+              [ "--ghc-option=-O2" "-fci" ]
               ++ lib.optionals stdenv.isLinux [
                 "--enable-executable-static"
                 "--extra-lib-dirs=${gmp.override { withStatic = true; }}/lib"
diff --git a/hevm.cabal b/hevm.cabal
index 9e259a6bd..f274d444e 100644
--- a/hevm.cabal
+++ b/hevm.cabal
@@ -40,11 +40,18 @@ extra-source-files:
   test/contracts/fail/dsProveFail.sol
   test/contracts/fail/invariantFail.sol
 
+flag ci
+  description: Sets flags for compilation in CI
+  default:     False
+  manual:      True
+
 source-repository head
   type:     git
   location: https://github.com/ethereum/hevm.git
 
 common shared
+  if flag(ci)
+    ghc-options: -Werror
   default-language:
     Haskell2010
   default-extensions:
@@ -287,6 +294,8 @@ common test-common
     test-base
   build-depends:
     test-utils
+  other-modules:
+    EVM.TestUtils
   if os(darwin)
     extra-libraries: c++
     -- https://gitlab.haskell.org/ghc/ghc/-/issues/11829
diff --git a/src/EVM/Dapp.hs b/src/EVM/Dapp.hs
index 79fef6a4a..9e37b38ab 100644
--- a/src/EVM/Dapp.hs
+++ b/src/EVM/Dapp.hs
@@ -68,7 +68,7 @@ dappInfo root solcByName sources =
   let
     solcs = Map.elems solcByName
     astIds = astIdMap $ snd <$> toList (view sourceAsts sources)
-    immutables = filter ((/=) mempty . _immutableReferences) solcs
+    immutables = filter ((/=) mempty . (view immutableReferences)) solcs
 
   in DappInfo
     { _dappRoot = root
diff --git a/src/EVM/Flatten.hs b/src/EVM/Flatten.hs
index 3d49ea289..2aedd2290 100644
--- a/src/EVM/Flatten.hs
+++ b/src/EVM/Flatten.hs
@@ -1,3 +1,5 @@
+{-# Language TupleSections #-}
+
 module EVM.Flatten (flatten) where
 
 -- This module concatenates all the imported dependencies
@@ -33,12 +35,12 @@ import qualified Data.Graph.Inductive.Query.DFS as Fgl
 import Data.SemVer (SemVerRange, parseSemVerRange)
 import qualified Data.SemVer as SemVer
 
-import Control.Monad (forM)
+import Control.Monad (forM, (>=>))
 import Data.ByteString (ByteString)
 import Data.Foldable (foldl', toList)
 import Data.List (sort, nub, (\\))
 import Data.Map (Map, (!), (!?))
-import Data.Maybe (mapMaybe, isJust, catMaybes, fromMaybe)
+import Data.Maybe (mapMaybe, isJust, fromMaybe)
 import Data.Text (Text, unpack, pack, intercalate)
 import Data.Text.Encoding (encodeUtf8, decodeUtf8)
 import Text.Read (readMaybe)
@@ -210,7 +212,7 @@ flatten dapp target = do
 
 joinLicenses :: [Value] -> Text
 joinLicenses asts =
-  case nub $ mapMaybe (\ast -> getAttribute "license" ast >>= preview _String) asts of
+  case nub $ mapMaybe (getAttribute "license" >=> preview _String) asts of
     [] -> ""
     x -> "// SPDX-License-Identifier: " <> intercalate " AND " x
 
@@ -248,9 +250,9 @@ maximalPragma asts = (
         ps = filter (nodeIs "PragmaDirective") (universe ast)
 
         components :: [[Value]]
-        components = catMaybes $
-          fmap
-          ((fmap toList) . (\x -> getAttribute "literals" x >>= preview _Array))
+        components = mapMaybe
+          ((fmap toList)
+             . (getAttribute "literals" >=> preview _Array))
           ps
 
     -- Simple way to combine many SemVer ranges.  We don't actually
@@ -400,9 +402,9 @@ prefixContractAst castr cs bso ast = prefixAstNodes
                   + (BS.length $ fst $ BS.breakSubstring name' bs')
                   + (BS.length name')
               in
-                fmap ((,) pos) $ id' v
+                fmap (pos,) $ id' v
             | t `elem` ["UserDefinedTypeName", "Identifier"] =
-              fmap ((,) end) $ refDec v
+              fmap (end,) $ refDec v
             | otherwise =
                 error $ "internal error: not a contract reference: " ++ show t
 
@@ -450,15 +452,16 @@ repeated :: Eq a => [a] -> [a]
 repeated = fmap fst $ foldl' f ([], [])
   where
     f (acc, seen) x =
-      ( if (x `elem` seen) && (not $ x `elem` acc)
+      ( if (x `elem` seen) && (x `notElem` acc)
         then x : acc
         else acc
       , x : seen
       )
 
 indexed :: [(Integer, Text)] -> [(Integer, Text)]
-indexed = fst . foldl' f ([], Map.empty) -- (zip (fmap snd xs) $ replicate (length xs) 0) xs
+indexed = fst . foldl' f ([], (Map.empty :: Map Text Integer))
   where
+    f :: (Show v, Num v, Ord k) => ([(a, Text)], Map k v) -> (a, k) -> ([(a, Text)], Map k v)
     f (acc, seen) (id', n) =
       let
         count = (fromMaybe 0 $ seen !? n) + 1
diff --git a/src/EVM/SMT.hs b/src/EVM/SMT.hs
index cadb206fe..c6778a2b9 100644
--- a/src/EVM/SMT.hs
+++ b/src/EVM/SMT.hs
@@ -25,7 +25,6 @@ import Language.SMT2.Syntax (SpecConstant(..), GeneralRes(..), Term(..), QualIde
 import Data.Word
 import Numeric (readHex)
 import Data.ByteString (ByteString)
-import Data.Maybe (fromMaybe)
 
 import qualified Data.ByteString as BS
 import qualified Data.List as List
@@ -785,10 +784,10 @@ parseFrameCtx name = case TS.unpack name of
   t -> error $ "Internal Error: cannot parse " <> t <> " into an Expr"
 
 getVars :: (TS.Text -> Expr EWord) -> SolverInstance -> [TS.Text] -> IO (Map (Expr EWord) W256)
-getVars parseFn inst names = Map.mapKeys parseFn <$> foldM getVar mempty names
+getVars parseFn inst names = Map.mapKeys parseFn <$> foldM getOne mempty names
   where
-    getVar :: Map TS.Text W256 -> TS.Text -> IO (Map TS.Text W256)
-    getVar acc name = do
+    getOne :: Map TS.Text W256 -> TS.Text -> IO (Map TS.Text W256)
+    getOne acc name = do
       raw <- getValue inst (T.fromStrict name)
       let
         parsed = case parseCommentFreeFileMsg getValueRes (T.toStrict raw) of
diff --git a/src/EVM/Solidity.hs b/src/EVM/Solidity.hs
index afdc6aed3..adc449592 100644
--- a/src/EVM/Solidity.hs
+++ b/src/EVM/Solidity.hs
@@ -47,6 +47,7 @@ module EVM.Solidity
   , sourceFiles
   , sourceLines
   , sourceAsts
+  , immutableReferences
   , stripBytecodeMetadata
   , stripBytecodeMetadataSym
   , signature
diff --git a/src/EVM/SymExec.hs b/src/EVM/SymExec.hs
index defeac8c9..766b04eea 100644
--- a/src/EVM/SymExec.hs
+++ b/src/EVM/SymExec.hs
@@ -528,9 +528,11 @@ equivalenceCheck solvers bytecodeA bytecodeB opts signature' = do
             (Revert _ a, Revert _ b) -> if a==b then PBool False else a ./= b
             (Revert _ _, _) -> PBool True
             (_, Revert _ _) -> PBool True
+            (Failure _ erra, Failure _ errb) -> if erra==errb then PBool False else PBool True
+            (GVar _, _) -> error "Expressions cannot contain global vars"
+            (_ , GVar _) -> error "Expressions cannot contain global vars"
             (Failure _ (TmpErr s), _) -> error $ "Unhandled error: " <> s
             (_, Failure _ (TmpErr s)) -> error $ "Unhandled error: " <> s
-            (Failure _ erra, Failure _ errb) -> if erra==errb then PBool False else PBool True
             (ITE _ _ _, _ ) -> error "Expressions must be flattened"
             (_, ITE _ _ _) -> error "Expressions must be flattened"
 
diff --git a/src/EVM/Transaction.hs b/src/EVM/Transaction.hs
index 0fe179b24..550706f61 100644
--- a/src/EVM/Transaction.hs
+++ b/src/EVM/Transaction.hs
@@ -163,7 +163,7 @@ instance FromJSON Transaction where
     toAddr   <- addrFieldMaybe val "to"
     v        <- wordField val "v"
     value    <- wordField val "value"
-    txType   <- fmap read <$> (val JSON..:? "type")
+    txType   <- fmap (read :: String -> Int) <$> (val JSON..:? "type")
     case txType of
       Just 0x00 -> return $ Transaction tdata gasLimit gasPrice nonce r s toAddr v value LegacyTransaction [] Nothing Nothing
       Just 0x01 -> do