diff --git a/js/js.libraries/src/core/domEventsCode.kt b/js/js.libraries/src/core/domEventsCode.kt
index edc18cfb02f..21dd77f628d 100644
--- a/js/js.libraries/src/core/domEventsCode.kt
+++ b/js/js.libraries/src/core/domEventsCode.kt
@@ -11,5 +11,5 @@ import org.w3c.dom.views.*
 */
 
 public trait EventListener {
-    public fun handleEvent(arg1: Event?): Unit
+    public fun handleEvent(arg1: Event): Unit
 }