diff --git a/composer.json b/composer.json
index b21275d..31f2e18 100644
--- a/composer.json
+++ b/composer.json
@@ -18,10 +18,11 @@
         "symfony/process": "^5.4|^6.3"
     },
     "require-dev": {
+        "matthiasnoback/symfony-config-test": "^5.0",
         "symfony/filesystem": "^6.3",
         "symfony/framework-bundle": "^6.3",
         "symfony/phpunit-bridge": "^6.3",
-        "phpstan/phpstan": "1.11.x-dev"
+        "phpstan/phpstan-symfony": "^1.4"
     },
     "minimum-stability": "dev",
     "autoload": {
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index ded42a0..5c3268e 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -1,10 +1,7 @@
+includes:
+        - vendor/phpstan/phpstan-symfony/extension.neon
+
 parameters:
-    level: 4
+    level: 5
     paths:
         - src
-
-    ignoreErrors:
-        -
-            message: "#^Call to an undefined method Symfony\\\\Component\\\\Config\\\\Definition\\\\Builder\\\\NodeParentInterface\\:\\:defaultValue\\(\\)\\.$#"
-            count: 1
-            path: src/DependencyInjection/SymfonycastsSassExtension.php
diff --git a/src/DependencyInjection/SymfonycastsSassExtension.php b/src/DependencyInjection/SymfonycastsSassExtension.php
index 3025038..c07d9a4 100644
--- a/src/DependencyInjection/SymfonycastsSassExtension.php
+++ b/src/DependencyInjection/SymfonycastsSassExtension.php
@@ -59,6 +59,22 @@ public function getConfigTreeBuilder(): TreeBuilder
                     ->cannotBeEmpty()
                     ->scalarPrototype()
                         ->end()
+                    ->validate()
+                        ->ifTrue(static function (array $paths): bool {
+                            if (1 === \count($paths)) {
+                                return false;
+                            }
+
+                            $filenames = [];
+                            foreach ($paths as $path) {
+                                $filename = basename($path, '.scss');
+                                $filenames[$filename] = $filename;
+                            }
+
+                            return \count($filenames) !== \count($paths);
+                        })
+                        ->thenInvalid('The "root_sass" paths need to end with unique filenames.')
+                        ->end()
                     ->defaultValue(['%kernel.project_dir%/assets/styles/app.scss'])
                 ->end()
                 ->scalarNode('binary')
diff --git a/tests/ConfigurationTest.php b/tests/ConfigurationTest.php
new file mode 100644
index 0000000..f1b724e
--- /dev/null
+++ b/tests/ConfigurationTest.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the SymfonyCasts SassBundle package.
+ * Copyright (c) SymfonyCasts <https://symfonycasts.com/>
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfonycasts\SassBundle\Tests;
+
+use Matthias\SymfonyConfigTest\PhpUnit\ConfigurationTestCaseTrait;
+use PHPUnit\Framework\TestCase;
+use Symfonycasts\SassBundle\DependencyInjection\SymfonycastsSassExtension;
+
+final class ConfigurationTest extends TestCase
+{
+    use ConfigurationTestCaseTrait;
+
+    protected function getConfiguration(): SymfonycastsSassExtension
+    {
+        return new SymfonycastsSassExtension();
+    }
+
+    public function testSingleSassRootPath(): void
+    {
+        $this->assertConfigurationIsValid([
+            'symfonycasts_sass' => [
+                'root_sass' => [
+                    '%kernel.project_dir%/assets/scss/app.scss',
+                ],
+            ],
+        ]);
+    }
+
+    public function testMultipleSassRootPaths(): void
+    {
+        $this->assertConfigurationIsValid([
+            'symfonycasts_sass' => [
+                'root_sass' => [
+                    '%kernel.project_dir%/assets/scss/app.scss',
+                    '%kernel.project_dir%/assets/admin/scss/admin.scss',
+                ],
+            ],
+        ]);
+    }
+
+    public function testMultipleSassRootPathsWithSameFilename(): void
+    {
+        $this->assertConfigurationIsInvalid([
+            'symfonycasts_sass' => [
+                'root_sass' => [
+                    '%kernel.project_dir%/assets/scss/app.scss',
+                    '%kernel.project_dir%/assets/admin/scss/app.scss',
+                ],
+            ],
+        ],
+            'Invalid configuration for path "symfonycasts_sass.root_sass": The "root_sass" paths need to end with unique filenames.');
+    }
+}