diff --git a/dead-code-detection.cabal b/dead-code-detection.cabal
--- a/dead-code-detection.cabal
+++ b/dead-code-detection.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           dead-code-detection
-version:        0.8
+version:        0.8.1
 synopsis:       detect dead code in haskell projects
 description:    detect dead code in haskell projects
 category:       Development
@@ -27,7 +27,8 @@
   hs-source-dirs:
       src
     , driver
-  ghc-options: -Wall -fno-warn-name-shadowing
+  ghc-options: -Wall -fno-warn-name-shadowing -fwarn-incomplete-uni-patterns -fwarn-incomplete-record-updates
+
   build-depends:
       base == 4.*
     , silently
@@ -57,7 +58,8 @@
   hs-source-dirs:
       test
     , src
-  ghc-options: -Wall -fno-warn-name-shadowing
+  ghc-options: -Wall -fno-warn-name-shadowing -fwarn-incomplete-record-updates
+
   build-depends:
       base == 4.*
     , silently
diff --git a/src/Ast.hs b/src/Ast.hs
--- a/src/Ast.hs
+++ b/src/Ast.hs
@@ -16,10 +16,11 @@
 
 import           Bag
 import           Control.Arrow ((>>>), second)
-import           Control.Exception
 import           Control.Monad
 import           Data.Data
 import           Data.Generics.Uniplate.Data
+import           ErrUtils
+import           Exception
 import qualified GHC
 import           GHC hiding (Module, moduleName)
 import           GHC.Paths (libdir)
@@ -31,6 +32,7 @@
 
 import           Ast.UsedNames
 import           Graph
+import           Utils
 
 type Ast = [Module]
 
@@ -60,8 +62,7 @@
 
 parse :: [FilePath] -> IO (Either String Ast)
 parse files =
-  errorHandler $
-  runGhc (Just libdir) $ do
+  runGhcPureExceptions $ do
     dynFlags <- getSessionDynFlags
     void $ setSessionDynFlags $ dynFlags {
       hscTarget = HscNothing,
@@ -82,18 +83,33 @@
           (parseModule mod >>= typecheckModule)
         return $ Just $ map toModule typecheckedModules
 
-errorHandler :: IO (Maybe a) -> IO (Either String a)
-errorHandler action =
+runGhcPureExceptions :: Ghc (Maybe a) -> IO (Either String a)
+runGhcPureExceptions action =
+  fmap (mapLeft (unlines . map stripSpaces)) $
+  captureStderr $
+  runGhc (Just libdir) $
   catchSourceError $
-  captureStderr action
+  fmap (maybe (Left []) Right) $
+  action
+
   where
+    captureStderr :: IO (Either [String] a) -> IO (Either [String] a)
     captureStderr action = do
       (errs, a) <- hCapture [stderr] action
-      return $ maybe (Left errs) Right a
+      return $ either (\ outerErrs -> Left (outerErrs ++ lines errs)) Right a
 
-    catchSourceError :: IO (Either String a) -> IO (Either String a)
-    catchSourceError = handle $ \ (e :: SourceError) ->
-      return $ Left $ show e
+    catchSourceError :: Ghc (Either [String] a) -> Ghc (Either [String] a)
+    catchSourceError = ghandle $ \ (e :: SourceError) -> do
+      dynFlags <- getSessionDynFlags
+      return $ Left [formatSourceError dynFlags e]
+
+formatSourceError :: DynFlags -> SourceError -> String
+formatSourceError dynFlags sourceError =
+  unlines $
+  map (showSDoc dynFlags) $
+  pprErrMsgBagWithLoc $
+  srcErrorMessages $
+  sourceError
 
 findExports :: Ast -> [ModuleName] -> Either String [Name]
 findExports ast names = concat <$> mapM inner names
diff --git a/src/Utils.hs b/src/Utils.hs
--- a/src/Utils.hs
+++ b/src/Utils.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
 module Utils where
@@ -28,3 +29,8 @@
 stripSpaces =
   reverse . dropWhile isSpace .
   reverse . dropWhile isSpace
+
+mapLeft :: (a -> b) -> Either a c -> Either b c
+mapLeft f = \ case
+  Left a -> Left $ f a
+  Right x -> Right x
diff --git a/test/AstSpec.hs b/test/AstSpec.hs
--- a/test/AstSpec.hs
+++ b/test/AstSpec.hs
@@ -31,6 +31,17 @@
         result <- parse ["Foo.hs"]
         void result `shouldBe` Left "\nFoo.hs:2:7: Not in scope: ‘bar’\n"
 
+    context "preprocessor errors" $ do
+      it "gives Lefts, not Exceptions" $ do
+        withFoo "{-# LANGUAGE CPP #-}\n#invalid" $ do
+          Left err <- parse ["Foo.hs"]
+          err `shouldContain` "lexical error"
+
+      it "includes source locations" $ do
+        withFoo "{-# LANGUAGE CPP #-}\n#invalid" $ do
+          Left err <- parse ["Foo.hs"]
+          err `shouldContain` "Foo.hs:2:2:"
+
     it "handles missing modules gracefully" $ do
       withFooHeader "import Bar" $ do
         Left message <- parse ["Foo.hs"]