diff --git a/src/Symfony/Component/Stopwatch/Stopwatch.php b/src/Symfony/Component/Stopwatch/Stopwatch.php
index 9da84f6ec0d7..e0024b0d1600 100644
--- a/src/Symfony/Component/Stopwatch/Stopwatch.php
+++ b/src/Symfony/Component/Stopwatch/Stopwatch.php
@@ -96,8 +96,8 @@ public function stopSection($id)
     /**
      * Starts an event.
      *
-     * @param string $name     The event name
-     * @param string $category The event category
+     * @param string      $name     The event name
+     * @param string|null $category The event category
      *
      * @return StopwatchEvent
      */
diff --git a/src/Symfony/Component/Stopwatch/Tests/StopwatchTest.php b/src/Symfony/Component/Stopwatch/Tests/StopwatchTest.php
index 10e6a14af62d..a5cb3dd92ae6 100644
--- a/src/Symfony/Component/Stopwatch/Tests/StopwatchTest.php
+++ b/src/Symfony/Component/Stopwatch/Tests/StopwatchTest.php
@@ -35,6 +35,14 @@ public function testStart()
         $this->assertSame($event, $stopwatch->getEvent('foo'));
     }
 
+    public function testStartWithoutCategory()
+    {
+        $stopwatch = new Stopwatch();
+        $stopwatchEvent = $stopwatch->start('bar');
+        $this->assertSame('default', $stopwatchEvent->getCategory());
+        $this->assertSame($stopwatchEvent, $stopwatch->getEvent('bar'));
+    }
+
     public function testIsStarted()
     {
         $stopwatch = new Stopwatch();