diff --git a/src/Symfony/Component/Console/Helper/DialogHelper.php b/src/Symfony/Component/Console/Helper/DialogHelper.php
index cf4d60ab858f..8d73addcf0e1 100644
--- a/src/Symfony/Component/Console/Helper/DialogHelper.php
+++ b/src/Symfony/Component/Console/Helper/DialogHelper.php
@@ -20,7 +20,7 @@
  */
 class DialogHelper extends Helper
 {
-    private $inputStream = STDIN;
+    private $inputStream;
 
     /**
      * Asks a question to the user.
@@ -35,7 +35,7 @@ public function ask(OutputInterface $output, $question, $default = null)
     {
         $output->write($question);
 
-        $ret = fgets($this->inputStream, 4096);
+        $ret = fgets($this->inputStream ?: STDIN, 4096);
         if (false === $ret) {
             throw new \RuntimeException('Aborted');
         }