diff --git a/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php b/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php
index e2c98b6889..e12c9a5973 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/CheckTypeDeclarationsPass.php
@@ -78,7 +78,7 @@ final class CheckTypeDeclarationsPass extends AbstractRecursivePass
     /**
      * {@inheritdoc}
      */
-    protected function processValue($value, $isRoot = false)
+    protected function processValue($value, bool $isRoot = false)
     {
         if (isset($this->skippedIds[$this->currentId])) {
             return $value;