diff --git a/src/Events/DI/EventsExtension.php b/src/Events/DI/EventsExtension.php
index 9edda33..b470188 100644
--- a/src/Events/DI/EventsExtension.php
+++ b/src/Events/DI/EventsExtension.php
@@ -383,7 +383,7 @@ private function optimizeListeners(DIContainerBuilder $builder)
 				// find all subclasses and register the listener to all the classes dispatching them
 				foreach ($builder->getDefinitions() as $def) {
 					$class = $def->getClass();
-					if (!empty($class)) {
+					if (!$class) {
 						continue; // ignore unresolved classes
 					}