diff --git a/force_bdss/core_mco_driver.py b/force_bdss/core_mco_driver.py
index cbb819d576956d311dc3b53f108b2803fa16a254..200993086a9d711b18f8fc6d140e13ef085aa88f 100644
--- a/force_bdss/core_mco_driver.py
+++ b/force_bdss/core_mco_driver.py
@@ -55,17 +55,17 @@ class CoreMCODriver(BaseCoreDriver):
 
     @on_trait_change("mco:started")
     def _deliver_start_event(self):
-        output_names = []
+        output_kpis = []
         for layer in self.workflow.execution_layers:
             for data_source in layer.data_sources:
-                output_names.extend(info.name
-                                    for info in data_source.output_slot_info
-                                    if info.is_kpi
-                                    )
+                output_kpis.extend(
+                    info for info in data_source.output_slot_info
+                    if info.is_kpi
+                )
 
         self._deliver_event(MCOStartEvent(
             input_names=tuple(p.name for p in self.workflow.mco.parameters),
-            output_names=tuple([on.name for on in output_names])
+            output_names=tuple([on.name for on in output_kpis])
         ))
 
     @on_trait_change("mco:finished")