diff --git a/tuned/monitors/repository.py b/tuned/monitors/repository.py
index 66dc84f..5bcbb75 100644
--- a/tuned/monitors/repository.py
+++ b/tuned/monitors/repository.py
@@ -25,7 +25,7 @@ class Repository(PluginLoader):
 		return monitor_instance
 
 	def delete(self, monitor):
-		assert isinstance(monitor, self._loader.interface)
+		assert isinstance(monitor, self._interface)
 		monitor.cleanup()
 		self._monitors.remove(monitor)