diff --git a/src/Symfony/Component/Debug/DebugClassLoader.php b/src/Symfony/Component/Debug/DebugClassLoader.php
index c5b78c90f2940..88e4890ead7cc 100644
--- a/src/Symfony/Component/Debug/DebugClassLoader.php
+++ b/src/Symfony/Component/Debug/DebugClassLoader.php
@@ -124,7 +124,10 @@ public static function disable()
         }
     }
 
-    public function findFile($class): ?string
+    /**
+     * @return string|null
+     */
+    public function findFile($class)
     {
         return $this->isFinder ? $this->classLoader[0]->findFile($class) ?: null : null;
     }