diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 44f7ed3..13010fc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -45,3 +45,43 @@ jobs:
           pnpm exec tsc --noEmit
           pnpm run build
           git diff --exit-code -- dist
+
+  # The suite again on PostgreSQL, which rejects SQL that SQLite accepts (0.2.0
+  # shipped a FOR UPDATE on an aggregate that no PostgreSQL install could run).
+  test-postgres:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:18
+        env:
+          POSTGRES_PASSWORD: postgres
+          POSTGRES_DB: testing
+        ports:
+          - 5432:5432
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 5s
+          --health-timeout 5s
+          --health-retries 10
+    env:
+      DB_CONNECTION: pgsql
+      DB_HOST: 127.0.0.1
+      DB_PORT: 5432
+      DB_DATABASE: testing
+      DB_USERNAME: postgres
+      DB_PASSWORD: postgres
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.4'
+          extensions: sodium, pdo_pgsql
+          coverage: none
+
+      - name: Install PHP dependencies
+        run: composer install --no-interaction --prefer-dist
+
+      - name: Test on PostgreSQL
+        run: composer run test
+
diff --git a/app/Application/TaskNumberSequence.php b/app/Application/TaskNumberSequence.php
index d9315ac..5656d05 100644
--- a/app/Application/TaskNumberSequence.php
+++ b/app/Application/TaskNumberSequence.php
@@ -10,8 +10,9 @@
 /**
  * Per-company task numbering.
  *
- * The number is `max(number) + 1` inside a transaction, which is portable
- * across MySQL, PostgreSQL and SQLite. Two concurrent writers can still agree
+ * The number is the highest one plus one, read inside a transaction. The row
+ * holding it is read and locked rather than `max()` taken, because PostgreSQL
+ * refuses FOR UPDATE on an aggregate. Two concurrent writers can still agree
  * on the same number; the unique index on `(company_id, number)` catches that
  * and TaskService retries once.
  */
@@ -22,8 +23,9 @@ public function next(int $companyId): int
         return DB::transaction(static function () use ($companyId): int {
             $highest = Task::query()
                 ->forCompany($companyId)
+                ->orderByDesc('number')
                 ->lockForUpdate()
-                ->max('number');
+                ->value('number');
 
             return (int) $highest + 1;
         });
diff --git a/module.json b/module.json
index 9ed16b2..2cd2469 100644
--- a/module.json
+++ b/module.json
@@ -18,7 +18,7 @@
     "requires": {},
     "schema_version": 2,
     "slug": "tasks-projects",
-    "version": "0.2.0",
+    "version": "0.2.1",
     "license": "AGPL-3.0-only",
     "compatibility": {
         "invoiceshelf": ">=3.0.0-alpha.2 <4.0.0",
diff --git a/package.json b/package.json
index ecca944..6b66dc8 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@invoiceshelf/module-tasks-projects",
-    "version": "0.2.0",
+    "version": "0.2.1",
     "private": true,
     "type": "module",
     "packageManager": "pnpm@11.6.0",
diff --git a/tests/TestCase.php b/tests/TestCase.php
index f432ea9..98d8d04 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -87,12 +87,27 @@ protected function getEnvironmentSetUp($app): void
     {
         $app['config']->set('app.key', 'base64:'.base64_encode(str_repeat('a', 32)));
         $app['config']->set('database.default', 'testing');
-        $app['config']->set('database.connections.testing', [
-            'driver' => 'sqlite',
-            'database' => ':memory:',
-            'prefix' => '',
-            'foreign_key_constraints' => true,
-        ]);
+        // SQLite in memory by default; CI also runs the suite on PostgreSQL,
+        // which refuses SQL that SQLite lets through (DB_CONNECTION=pgsql).
+        $app['config']->set('database.connections.testing', getenv('DB_CONNECTION') === 'pgsql'
+            ? [
+                'driver' => 'pgsql',
+                'host' => getenv('DB_HOST') ?: '127.0.0.1',
+                'port' => (int) (getenv('DB_PORT') ?: 5432),
+                'database' => getenv('DB_DATABASE') ?: 'testing',
+                'username' => getenv('DB_USERNAME') ?: 'postgres',
+                'password' => getenv('DB_PASSWORD') ?: '',
+                'charset' => 'utf8',
+                'prefix' => '',
+                'schema' => 'public',
+                'sslmode' => 'prefer',
+            ]
+            : [
+                'driver' => 'sqlite',
+                'database' => ':memory:',
+                'prefix' => '',
+                'foreign_key_constraints' => true,
+            ]);
     }
 
     /**