diff --git a/idea/idea-analysis/src/org/jetbrains/kotlin/idea/caches/PerModulePackageCacheService.kt b/idea/idea-analysis/src/org/jetbrains/kotlin/idea/caches/PerModulePackageCacheService.kt
index e19244e8309..475758eabfd 100644
--- a/idea/idea-analysis/src/org/jetbrains/kotlin/idea/caches/PerModulePackageCacheService.kt
+++ b/idea/idea-analysis/src/org/jetbrains/kotlin/idea/caches/PerModulePackageCacheService.kt
@@ -74,7 +74,7 @@ class KotlinPackageContentModificationListener(private val project: Project) {
         })
 
         connection.subscribe(ProjectTopics.PROJECT_ROOTS, object : ModuleRootListener {
-            override fun rootsChanged(event: ModuleRootEvent?) {
+            override fun rootsChanged(event: ModuleRootEvent) {
                 PerModulePackageCacheService.getInstance(project).onTooComplexChange()
             }
         })