diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c5d467f..0f15b20 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -110,7 +110,7 @@ jobs:
 
             - name: Get composer cache directory
               id: composer-cache
-              run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+              run: echo "dir=$(composer config cache-files-dir)" >> "$GITHUB_OUTPUT"
 
             - name: Cache composer dependencies
               uses: actions/cache@v5
@@ -120,7 +120,8 @@ jobs:
                   restore-keys: ${{ runner.os }}-composer-
 
             - name: Allow dev dependencies
-              run: if [ "${{ matrix.minimum-stability }}" = "dev" ]; then perl -pi -e 's/^}$/,"minimum-stability":"dev","prefer-stable":true}/' composer.json; fi;
+              if: matrix.minimum-stability == 'dev'
+              run: composer config minimum-stability dev && composer config prefer-stable true
 
             - name: Install Composer dependencies
               run: composer update --prefer-dist --no-interaction ${{ matrix.composer-flags }}
diff --git a/.gitignore b/.gitignore
index f218929..e093cc1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,6 @@
 # Third party
 /.php-cs-fixer.cache
-/.phpunit.result.cache
+/.phpunit.cache
 /composer.lock
 /vendor
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index e19d60d..190f9de 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 * Added support for Symfony 8.2
 * Replaced the `gifexception:optimize` command and `bin/optimizer.php` by the `castor optimize` task
+* Upgraded the test suite to PHPUnit 11
 
 ## 1.11.1 (2026-05-26)
 
diff --git a/castor.php b/castor.php
index 328c439..daa8a90 100644
--- a/castor.php
+++ b/castor.php
@@ -29,7 +29,7 @@ function cs(bool $dryRun = false): void
 #[AsTask(description: 'Run the test suite')]
 function test(): void
 {
-    run('vendor/bin/simple-phpunit');
+    run('vendor/bin/phpunit');
 }
 
 #[AsTask(description: 'Run static analysis')]
diff --git a/composer.json b/composer.json
index d6f4fbd..6450ee2 100644
--- a/composer.json
+++ b/composer.json
@@ -26,6 +26,7 @@
         "doctrine/annotations": "^2.0",
         "friendsofphp/php-cs-fixer": "^3.17",
         "phpstan/phpstan": "^2.1",
+        "phpunit/phpunit": "^11.5",
         "symfony/asset": "^6.4 || ^7.3 || ^8.0",
         "symfony/browser-kit": "^6.4 || ^7.3 || ^8.0",
         "symfony/config": "^6.4 || ^7.3 || ^8.0",
@@ -34,7 +35,7 @@
         "symfony/error-handler": "^6.4 || ^7.3 || ^8.0",
         "symfony/http-kernel": "^6.4 || ^7.3 || ^8.0",
         "symfony/monolog-bundle": "^3.8 || ^4.0",
-        "symfony/phpunit-bridge": "^6.3 || ^7.0",
+        "symfony/phpunit-bridge": "^7.3 || ^8.0",
         "symfony/stopwatch": "^6.4 || ^7.3 || ^8.0",
         "symfony/web-profiler-bundle": "^6.4 || ^7.3 || ^8.0",
         "symfony/yaml": "^6.4 || ^7.3 || ^8.0"
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 59cabc2..986d8ed 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,22 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- http://phpunit.de/manual/current/en/appendixes.configuration.html -->
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="./vendor/bin/.phpunit/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
          backupGlobals="false"
          bootstrap="tests/app/bootstrap.php"
+         cacheDirectory=".phpunit.cache"
          colors="true"
          failOnRisky="true"
          failOnWarning="true"
 >
-    <coverage processUncoveredFiles="true">
-        <include>
-            <directory>.</directory>
-        </include>
-        <exclude>
-            <directory>tests</directory>
-            <directory>vendor</directory>
-        </exclude>
-    </coverage>
     <php>
         <ini name="display_errors" value="1" />
         <ini name="error_reporting" value="-1" />
@@ -30,4 +21,16 @@
             <directory>tests</directory>
         </testsuite>
     </testsuites>
+    <source>
+        <include>
+            <directory>.</directory>
+        </include>
+        <exclude>
+            <directory>tests</directory>
+            <directory>vendor</directory>
+        </exclude>
+    </source>
+    <extensions>
+        <bootstrap class="Symfony\Bridge\PhpUnit\SymfonyExtension" />
+    </extensions>
 </phpunit>
diff --git a/tests/FunctionalTest.php b/tests/FunctionalTest.php
index 5343c51..a37040e 100644
--- a/tests/FunctionalTest.php
+++ b/tests/FunctionalTest.php
@@ -17,6 +17,26 @@
 
 class FunctionalTest extends WebTestCase
 {
+    protected function tearDown(): void
+    {
+        parent::tearDown();
+
+        // FrameworkBundle::boot() calls ErrorHandler::register() on every kernel boot. Before
+        // symfony/error-handler 8.1, it left an exception handler registered when another error
+        // handler (PHPUnit's) was already in charge, which PHPUnit reports as a risky test.
+        // Remove this once Symfony < 8.1 is dropped.
+        while (true) {
+            $previous = set_exception_handler(static fn () => null);
+            restore_exception_handler();
+
+            if (null === $previous) {
+                break;
+            }
+
+            restore_exception_handler();
+        }
+    }
+
     public function testItDoesNotDisplayGifOnExceptionPageIfTheBundleIsNotEnabled(): void
     {
         $client = static::createClient(['environment' => 'prod', 'debug' => true]);