diff --git a/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php b/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php
index 37f8fb73cd217..12c38153a26f4 100644
--- a/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php
+++ b/src/Symfony/Component/HttpKernel/DataCollector/ConfigDataCollector.php
@@ -219,7 +219,7 @@ public function getEnv()
     /**
      * Returns true if the debug is enabled.
      *
-     * @return bool true if debug is enabled, false otherwise
+     * @return bool|string true if debug is enabled, false otherwise or a string if no kernel was set
      */
     public function isDebug()
     {