diff --git a/.github/settings.yml b/.github/settings.yml
index ae50b5d2..aac834e0 100644
--- a/.github/settings.yml
+++ b/.github/settings.yml
@@ -30,6 +30,9 @@ branches:
           - context: "Tests (8.3, highest)"
           - context: "Tests (8.3, locked)"
           - context: "Tests (8.3, lowest)"
+          - context: "Tests (8.4, highest)"
+          - context: "Tests (8.4, locked)"
+          - context: "Tests (8.4, lowest)"
         strict: false
       restrictions:
 
diff --git a/.github/workflows/integrate.yaml b/.github/workflows/integrate.yaml
index df540a61..b8d9b7c1 100644
--- a/.github/workflows/integrate.yaml
+++ b/.github/workflows/integrate.yaml
@@ -420,6 +420,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
 
         dependencies:
           - "lowest"
@@ -456,6 +457,10 @@ jobs:
           key: "php-${{ matrix.php-version }}-composer-${{ matrix.dependencies }}-${{ hashFiles('composer.lock') }}"
           restore-keys: "php-${{ matrix.php-version }}-composer-${{ matrix.dependencies }}-"
 
+      - name: "Remove incompatible dependencies with composer"
+        if: "matrix.dependencies != 'locked'"
+        run: "composer remove roave/backward-compatibility-check --ansi --dev --no-interaction --no-progress"
+
       - name: "Remove platform configuration with composer"
         if: "matrix.dependencies != 'locked'"
         run: "composer config platform.php --ansi --unset"
diff --git a/composer.json b/composer.json
index b9ef1c68..b1939332 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
     "security": "https://github.com/ergebnis/php-cs-fixer-config-template/blob/main/.github/SECURITY.md"
   },
   "require": {
-    "php": "~8.1.0 || ~8.2.0 || ~8.3.0",
+    "php": "~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0",
     "friendsofphp/php-cs-fixer": "~3.64.0"
   },
   "require-dev": {
diff --git a/composer.lock b/composer.lock
index 7e35ee38..92d47dd6 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "ad562b51ae7056aee2cbf3f4548ad84a",
+    "content-hash": "7f4b78f143a22edea17ddf604fee4aa9",
     "packages": [
         {
             "name": "clue/ndjson-react",
@@ -6512,13 +6512,13 @@
     ],
     "aliases": [],
     "minimum-stability": "stable",
-    "stability-flags": [],
+    "stability-flags": {},
     "prefer-stable": false,
     "prefer-lowest": false,
     "platform": {
-        "php": "~8.1.0 || ~8.2.0 || ~8.3.0"
+        "php": "~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0"
     },
-    "platform-dev": [],
+    "platform-dev": {},
     "platform-overrides": {
         "php": "8.1.26"
     },
diff --git a/test/EndToEnd/RuleSet/AbstractRuleSetTestCase.php b/test/EndToEnd/RuleSet/AbstractRuleSetTestCase.php
index 1131f997..e2b91be1 100644
--- a/test/EndToEnd/RuleSet/AbstractRuleSetTestCase.php
+++ b/test/EndToEnd/RuleSet/AbstractRuleSetTestCase.php
@@ -38,6 +38,17 @@ final protected function tearDown(): void
 
     final public function testConfigurationIsConsideredValid(): void
     {
+        $env = [];
+
+        if (PHP_VERSION_ID >= 80400) {
+            $env = [
+                /**
+                 * @see https://github.com/PHP-CS-Fixer/PHP-CS-Fixer/blob/v3.64.0/README.md#supported-php-versions
+                 */
+                'PHP_CS_FIXER_IGNORE_ENV' => true,
+            ];
+        }
+
         $process = new Process\Process(
             [
                 'vendor/bin/php-cs-fixer',
@@ -49,7 +60,8 @@ final public function testConfigurationIsConsideredValid(): void
                 '--dry-run',
                 self::configPath(),
             ],
-            null
+            null,
+            $env,
         );
 
         $process->run();