diff --git a/hpp.cabal b/hpp.cabal
--- a/hpp.cabal
+++ b/hpp.cabal
@@ -1,5 +1,5 @@
 name:                hpp
-version:             0.6.1
+version:             0.6.2
 synopsis:            A Haskell pre-processor
 description:         See the README for usage examples
 license:             BSD3
@@ -12,7 +12,7 @@
 extra-source-files:  tests/mcpp-validation.sh, CHANGELOG.md, README.md
 cabal-version:       >=1.10
 homepage:            https://github.com/acowley/hpp
-tested-with:         GHC == 7.10.3, GHC == 8.0.2, GHC == 8.2.2, GHC == 8.4.3
+tested-with:         GHC == 8.4.4 || == 8.6.5 || == 8.8.2
 
 source-repository head
   type:     git
@@ -35,12 +35,12 @@
                        Hpp.StringSig,
                        Hpp.Tokens,
                        Hpp.Types
-  build-depends:       base >=4.8 && <4.13, directory, time >=1.5, filepath,
+  build-depends:       base >=4.8 && < 4.14, directory, time >=1.5, filepath,
                        transformers >=0.4, bytestring, unordered-containers,
                        ghc-prim
 
   if impl(ghc < 8)
-    build-depends: semigroups >= 0.18 && < 0.19
+    build-depends: semigroups >= 0.18 && < 0.20
 
   hs-source-dirs:      src
   default-language:    Haskell2010
diff --git a/src/Hpp/CmdLine.hs b/src/Hpp/CmdLine.hs
--- a/src/Hpp/CmdLine.hs
+++ b/src/Hpp/CmdLine.hs
@@ -85,6 +85,8 @@
           go env acc cfg out rst -- We ignore source language specification
         go env acc cfg out ("-traditional":rst) =
           go env acc cfg out rst -- Ignore the "-traditional" flag
+        go env acc cfg out ("-Werror":rst) =
+          go env acc cfg out rst -- Ignore the "-Werror" flag
         go env acc cfg Nothing (file:rst) =
           case curFileNameF cfg of
             Nothing -> go env acc (cfg { curFileNameF = Just file }) Nothing rst
diff --git a/src/Hpp/Expansion.hs b/src/Hpp/Expansion.hs
--- a/src/Hpp/Expansion.hs
+++ b/src/Hpp/Expansion.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE LambdaCase, OverloadedStrings, RankNTypes, ScopedTypeVariables #-}
+{-# LANGUAGE CPP, LambdaCase, OverloadedStrings, RankNTypes, ScopedTypeVariables #-}
 -- | Line expansion is the core input token processing
 -- logic. Object-like macros are substituted, and function-like macro
 -- applications are expanded.
@@ -8,7 +8,9 @@
 import Data.Foldable (foldl', traverse_)
 import Data.List (delete)
 import Data.Maybe (listToMaybe, mapMaybe)
+#if __GLASGOW_HASKELL__ < 808
 import Data.Monoid ((<>))
+#endif
 import Data.String (fromString)
 import Hpp.Config (Config, curFileName,
                    getDateString, getTimeString, prepDate, prepTime)
diff --git a/src/Hpp/Tokens.hs b/src/Hpp/Tokens.hs
--- a/src/Hpp/Tokens.hs
+++ b/src/Hpp/Tokens.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE BangPatterns, OverloadedStrings, ViewPatterns #-}
+{-# LANGUAGE BangPatterns, CPP, OverloadedStrings, ViewPatterns #-}
 -- | Tokenization breaks a 'String' into pieces of whitespace,
 -- constants, symbols, and identifiers.
 module Hpp.Tokens (Token(..), detok, isImportant, notImportant, importants,
@@ -7,7 +7,9 @@
 import Control.Arrow (first, second)
 import Data.Char (isAlphaNum, isDigit, isSpace, isOctDigit, isHexDigit, digitToInt)
 import Data.Foldable (foldl')
+#if __GLASGOW_HASKELL__ < 808
 import Data.Monoid ((<>))
+#endif
 import Data.String (IsString, fromString)
 import Hpp.StringSig
 
diff --git a/tests/mcpp-validation.sh b/tests/mcpp-validation.sh
--- a/tests/mcpp-validation.sh
+++ b/tests/mcpp-validation.sh
@@ -3,6 +3,7 @@
 HOST='http://prdownloads.sourceforge.net/mcpp/mcpp-2.7.2.tar.gz?download'
 FILE='mcpp-2.7.2.tar.gz'
 GCC=gcc
+CABAL=${CABALBUILD:-cabal v2-build}
 
 # Note: head -n -1 would be faster than "sed '$ d'", but doesn't work
 # with BSD or OS X head.
@@ -32,11 +33,7 @@
 fi
 
 echo 'Building hpp'
-if [ -z "$TRAVIS" ]; then
-  (cd .. && stack build hpp:hpp)
-else
-  (cd .. && cabal new-build)
-fi
+(cd .. && ${CABAL})
 if ! [ $? -eq 0 ]; then
   echo 'Building hpp failed'
   exit 1
@@ -52,18 +49,11 @@
 # Note that we define __i386__ as the architecture as the MCPP
 # validation test n_12.c assumes a long is 32 bits.
 
-
 if [ -z "$TRAVIS" ]; then
-  case $(uname -s) in
-      Darwin)
-          (cd mcpp-2.7.2/test-c &&  ../tool/cpp_test HPP "$(cd ../../.. && stack exec which -- hpp) -I/usr/include ${GCCDIR} --cpp -D__i386__ -D__DARWIN_ONLY_UNIX_CONFORMANCE %s.c | gcc -o %s -w -x c -" "rm %s" < n_i_.lst)
-          ;;
-      *) (cd mcpp-2.7.2/test-c &&  ../tool/cpp_test HPP "$(find $(pwd)/../../../.stack-work -type f -executable -name hpp -print -quit) ${GCCDIR} --cpp -D__x86_64__ %s.c | gcc -o %s -w -x c -" "rm %s" < n_i_.lst)
-  esac
+    (cd mcpp-2.7.2/test-c &&  ../tool/cpp_test HPP "$(find $(pwd)/../../../dist-newstyle -type f -executable -name hpp) ${GCCDIR} --cpp -D__x86_64__ %s.c | gcc -o %s -w -x c -" "rm %s" < n_i_.lst)
 else
-  (cd mcpp-2.7.2/test-c &&  ../tool/cpp_test HPP "$(find $(pwd)/../../../../dist-newstyle -type f -executable -name hpp) ${GCCDIR} --cpp -D__x86_64__ %s.c | gcc -o %s -w -x c -" "rm %s" < n_i_.lst)
-fi
-
+    (cd mcpp-2.7.2/test-c &&  ../tool/cpp_test HPP "$(find $(pwd)/../../../../dist-newstyle -type f -executable -name hpp) ${GCCDIR} --cpp -D__x86_64__ %s.c | gcc -o %s -w -x c -" "rm %s" < n_i_.lst)
+fi    
 if ! [ $? -eq 0 ]; then
   echo 'The test runner exited with an error.'
   exit 1