diff --git a/src/Symfony/Component/Console/Helper/ProgressBar.php b/src/Symfony/Component/Console/Helper/ProgressBar.php
index 1b2eefd29e..261141ff1d 100644
--- a/src/Symfony/Component/Console/Helper/ProgressBar.php
+++ b/src/Symfony/Component/Console/Helper/ProgressBar.php
@@ -41,7 +41,7 @@ class ProgressBar
     private $stepWidth;
     private $percent = 0.0;
     private $formatLineCount;
-    private $messages;
+    private $messages = array();
     private $overwrite = true;
 
     private static $formatters;
@@ -139,6 +139,16 @@ class ProgressBar
         return isset(self::$formats[$name]) ? self::$formats[$name] : null;
     }
 
+    /**
+     * Associates a text with a named placeholder.
+     *
+     * The text is displayed when the progress bar is rendered but only
+     * when the corresponding placeholder is part of the custom format line
+     * (by wrapping the name with %).
+     *
+     * @param string $message The text to associate with the placeholder
+     * @param string $name    The name of the placeholder
+     */
     public function setMessage($message, $name = 'message')
     {
         $this->messages[$name] = $message;