diff --git a/.github/workflows/haskell-ci.yml b/.github/workflows/haskell-ci.yml
index 133f7a5..bb506c7 100644
--- a/.github/workflows/haskell-ci.yml
+++ b/.github/workflows/haskell-ci.yml
@@ -207,6 +207,8 @@ jobs:
           echo "packages: ${PKGDIR_tree_diff}" >> cabal.project
           echo "package tree-diff" >> cabal.project
           echo "    ghc-options: -Werror=missing-methods -Werror=missing-fields" >> cabal.project
+          if [ $((HCNUMVER >= 90400)) -ne 0 ] ; then echo "package tree-diff" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
           cat >> cabal.project <<EOF
           EOF
           $HCPKG list --simple-output --names-only | perl -ne 'for (split /\s+/) { print "constraints: any.$_ installed\n" unless /^(tree-diff)$/; }' >> cabal.project.local
diff --git a/cabal.haskell-ci b/cabal.haskell-ci
index 307092d..4f3666d 100644
--- a/cabal.haskell-ci
+++ b/cabal.haskell-ci
@@ -2,7 +2,6 @@ branches: master
 tests:    >=7.6
 haddock:  >=7.8
 docspec:  >=8
-error-unused-packages: False
 
 -- We would like to have this. But it just doesn't work with GHCJS
 -- constraint-set bytestring-0.11
diff --git a/tree-diff.cabal b/tree-diff.cabal
index 9f5ec6a..d589209 100644
--- a/tree-diff.cabal
+++ b/tree-diff.cabal
@@ -134,13 +134,11 @@ test-suite tree-diff-test
 
   -- dependencies from library
   build-depends:
-    , ansi-terminal
     , ansi-wl-pprint
     , base
     , parsec
     , primitive
     , QuickCheck
-    , tagged
     , tree-diff
     , unordered-containers