diff --git a/src/EventRegistry.php b/src/EventRegistry.php
index 7c4a5f64c..3231f9c7f 100644
--- a/src/EventRegistry.php
+++ b/src/EventRegistry.php
@@ -125,6 +125,11 @@ public function getAllActiveEvents(): array
      */
     public function getEventClassName(string $event)
     {
+        // if the event is already a class name, use it
+        if (class_exists($event)) {
+            return $event;
+        }
+
         if (isset(self::$eventsMap[$event])) {
             return self::$eventsMap[$event];
         }
diff --git a/tests/EventRegistryTest.php b/tests/EventRegistryTest.php
index 139da0c10..5326d622a 100644
--- a/tests/EventRegistryTest.php
+++ b/tests/EventRegistryTest.php
@@ -15,6 +15,7 @@
 use Symfony\Bundle\MakerBundle\EventRegistry;
 use Symfony\Component\Console\Event\ConsoleCommandEvent;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
+use Symfony\Component\HttpKernel\Event\ControllerEvent;
 use Symfony\Component\HttpKernel\Event\ExceptionEvent;
 use Symfony\Component\HttpKernel\KernelEvents;
 
@@ -84,6 +85,14 @@ public function testGetNewEventClassNameFromStandardList()
         $registry = new EventRegistry($dispatcher);
         $this->assertSame(ExceptionEvent::class, $registry->getEventClassName(KernelEvents::EXCEPTION));
     }
+
+    public function testGetEventClassNameGivenEventAsClass()
+    {
+        $dispatcher = $this->createMock(EventDispatcherInterface::class);
+
+        $registry = new EventRegistry($dispatcher);
+        $this->assertSame(ControllerEvent::class, $registry->getEventClassName(ControllerEvent::class));
+    }
 }
 
 class DummyEvent