diff --git a/.github/workflows/haskell-ci.yml b/.github/workflows/haskell-ci.yml
index 0b0e5eef..5883ebc8 100644
--- a/.github/workflows/haskell-ci.yml
+++ b/.github/workflows/haskell-ci.yml
@@ -229,6 +229,10 @@ jobs:
           if [ $((HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
           if [ $((HCNUMVER >= 90400)) -ne 0 ] ; then echo "package cabal-install-parsers" >> cabal.project ; fi
           if [ $((HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 90000)) -ne 0 ] ; then echo "package haskell-ci" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 90000)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 90000)) -ne 0 ] ; then echo "package cabal-install-parsers" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 90000)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
           cat >> cabal.project <<EOF
           allow-newer: ShellCheck:filepath
 
diff --git a/cabal-install-parsers/test/Golden.hs b/cabal-install-parsers/test/Golden.hs
index d817b360..96cebc3b 100644
--- a/cabal-install-parsers/test/Golden.hs
+++ b/cabal-install-parsers/test/Golden.hs
@@ -65,3 +65,4 @@ instance ToExpr Doc where
 instance ToExpr (PrettyField ann) where
   toExpr (PrettyField _ fn d)       = App "PrettyField"   [toExpr fn, toExpr d]
   toExpr (PrettySection _ fn ds ps) = App "PrettySection" [toExpr fn, toExpr ds, toExpr ps]
+  toExpr PrettyEmpty                = App "PrettyEmpty"   []
diff --git a/fixtures/all-versions.github b/fixtures/all-versions.github
index 0c144426..852ecdad 100644
--- a/fixtures/all-versions.github
+++ b/fixtures/all-versions.github
@@ -445,6 +445,8 @@ jobs:
           if [ $((GHCJSARITH || ! GHCJSARITH && HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods -Werror=missing-fields" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> 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 /^(splitmix)$/; }' >> cabal.project.local
diff --git a/fixtures/doctest-version.github b/fixtures/doctest-version.github
index e9887a24..e58376b2 100644
--- a/fixtures/doctest-version.github
+++ b/fixtures/doctest-version.github
@@ -460,6 +460,8 @@ jobs:
           if [ $((GHCJSARITH || ! GHCJSARITH && HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods -Werror=missing-fields" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> 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 /^(splitmix)$/; }' >> cabal.project.local
diff --git a/fixtures/doctest.github b/fixtures/doctest.github
index 57d7624b..a76d7c81 100644
--- a/fixtures/doctest.github
+++ b/fixtures/doctest.github
@@ -460,6 +460,8 @@ jobs:
           if [ $((GHCJSARITH || ! GHCJSARITH && HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods -Werror=missing-fields" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> 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 /^(splitmix)$/; }' >> cabal.project.local
diff --git a/fixtures/empty-line.github b/fixtures/empty-line.github
index d712e699..4c3578ae 100644
--- a/fixtures/empty-line.github
+++ b/fixtures/empty-line.github
@@ -302,6 +302,14 @@ jobs:
           if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
           if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-server" >> cabal.project ; fi
           if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-client" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-docs" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-server" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
           cat >> cabal.project <<EOF
           constraints: foundatiion >= 0.14
           allow-newer: servant-js:servant
diff --git a/fixtures/enabled-jobs.github b/fixtures/enabled-jobs.github
index 1e6f1988..1baf7735 100644
--- a/fixtures/enabled-jobs.github
+++ b/fixtures/enabled-jobs.github
@@ -445,6 +445,8 @@ jobs:
           if [ $((GHCJSARITH || ! GHCJSARITH && HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods -Werror=missing-fields" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
           if [ $((! GHCJSARITH && HCNUMVER >= 90400)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "package splitmix" >> cabal.project ; fi
+          if [ $((! GHCJSARITH && HCNUMVER >= 90000)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> 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 /^(splitmix)$/; }' >> cabal.project.local
diff --git a/fixtures/messy.github b/fixtures/messy.github
index 22a91cfd..0c5e4d79 100644
--- a/fixtures/messy.github
+++ b/fixtures/messy.github
@@ -303,6 +303,14 @@ jobs:
           if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
           if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-server" >> cabal.project ; fi
           if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=unused-packages" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-client" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-docs" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "package servant-server" >> cabal.project ; fi
+          if [ $((HCNUMVER > 81007)) -ne 0 ] ; then echo "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns" >> cabal.project ; fi
           cat >> cabal.project <<EOF
           EOF
           if $HEADHACKAGE; then
diff --git a/haskell-ci.cabal b/haskell-ci.cabal
index b8f93452..67c198d9 100644
--- a/haskell-ci.cabal
+++ b/haskell-ci.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.2
 name:               haskell-ci
-version:            0.19.20250708
+version:            0.19.20250710
 synopsis:           Haskell CI script generator
 description:
   Script generator (@haskell-ci@) for
diff --git a/src/HaskellCI/Config/Grammar.hs b/src/HaskellCI/Config/Grammar.hs
index 6104aa25..40eee086 100644
--- a/src/HaskellCI/Config/Grammar.hs
+++ b/src/HaskellCI/Config/Grammar.hs
@@ -165,6 +165,8 @@ configGrammar = Config
         ^^^ metahelp "PKGSCOPE" "Insert -Werror=missing-methods for package scope (none, local, all)"
     <*> rangeField         "error-unused-packages"                                         (field @"cfgErrorUnusedPkgs") defaultConfig
         ^^^ metahelp "RANGE" "Insert -Werror=unused-packages"
+    <*> rangeField         "error-incomplete-patterns"                                     (field @"cfgErrorIncompletePatterns") defaultConfig
+        ^^^ metahelp "RANGE" "Insert -Werror=incomplete-(uni-)patterns"
     <*> blurFieldGrammar (field @"cfgDoctest") doctestConfigGrammar defaultConfig
     <*> blurFieldGrammar (field @"cfgDocspec") docspecConfigGrammar defaultConfig
     <*> pure [] -- constraint sets
diff --git a/src/HaskellCI/Config/History.hs b/src/HaskellCI/Config/History.hs
index e40bd209..63f09549 100644
--- a/src/HaskellCI/Config/History.hs
+++ b/src/HaskellCI/Config/History.hs
@@ -85,6 +85,8 @@ configHistory =
         & field @"cfgDocspec" . field @"cfgDocspecHash" .~ "cc20bb5c19501b42bde77556bc419c7c0a5c8d1eb65663024d8a4e4c868bef25"
     , ver 0 19 20250708 := \cfg -> cfg
         & field @"cfgErrorUnusedPkgs" .~ C.orLaterVersion (C.mkVersion [9,4])
+    , ver 0 19 20250108 := \cfg -> cfg
+        & field @"cfgErrorIncompletePatterns" .~ C.orLaterVersion (C.mkVersion [9,0])
     ]
   where
     ver x y z = [x, y, z]
diff --git a/src/HaskellCI/Config/Initial.hs b/src/HaskellCI/Config/Initial.hs
index 4107e7e3..0a94ba46 100644
--- a/src/HaskellCI/Config/Initial.hs
+++ b/src/HaskellCI/Config/Initial.hs
@@ -75,6 +75,7 @@ initialConfig = Config
     , cfgInsertVersion       = True
     , cfgErrorMissingMethods = PackageScopeLocal
     , cfgErrorUnusedPkgs     = noVersion
+    , cfgErrorIncompletePatterns = noVersion
     , cfgDoctest             = initialDoctestConfig
     , cfgDocspec             = initialDocspecConfig
     , cfgConstraintSets      = []
diff --git a/src/HaskellCI/Config/Type.hs b/src/HaskellCI/Config/Type.hs
index 8e06bc44..dbc3a930 100644
--- a/src/HaskellCI/Config/Type.hs
+++ b/src/HaskellCI/Config/Type.hs
@@ -75,6 +75,7 @@ data Config = Config
     , cfgInsertVersion       :: !Bool
     , cfgErrorMissingMethods :: !PackageScope
     , cfgErrorUnusedPkgs     :: !VersionRange
+    , cfgErrorIncompletePatterns :: !VersionRange
     , cfgDoctest             :: !DoctestConfig
     , cfgDocspec             :: !DocspecConfig
     , cfgConstraintSets      :: [ConstraintSet]
diff --git a/src/HaskellCI/GitHub.hs b/src/HaskellCI/GitHub.hs
index 9ce1acf7..56dcc496 100644
--- a/src/HaskellCI/GitHub.hs
+++ b/src/HaskellCI/GitHub.hs
@@ -363,6 +363,13 @@ makeGitHub _argv config@Config {..} gitconfig prj jobs@JobVersions {..} = do
                 echo_if_to range "cabal.project" $ "package " ++ pkgName
                 echo_if_to range "cabal.project" $ "    ghc-options: -Werror=unused-packages"
 
+            -- -Werror-unused-pkgs
+            for_ pkgs $ \Pkg{pkgName,pkgJobs} -> do
+                -- is introduced in 8.10.
+                let range = Range cfgErrorIncompletePatterns /\ RangePoints pkgJobs
+                echo_if_to range "cabal.project" $ "package " ++ pkgName
+                echo_if_to range "cabal.project" $ "    ghc-options: -Werror=incomplete-patterns -Werror=incomplete-uni-patterns"
+
             -- extra cabal.project fields
             cat "cabal.project" $ C.showFields' (const C.NoComment) (const id) 2 $ extraCabalProjectFields "$GITHUB_WORKSPACE/source/"