diff --git a/SAS/TMSS/backend/src/tmss/tmssapp/models/specification.py b/SAS/TMSS/backend/src/tmss/tmssapp/models/specification.py
index d28d2747f3d5f434379cfa82e28d3adb48e54f89..621c1f82ff7faf396782bd636b1d2f578e181701 100644
--- a/SAS/TMSS/backend/src/tmss/tmssapp/models/specification.py
+++ b/SAS/TMSS/backend/src/tmss/tmssapp/models/specification.py
@@ -1699,7 +1699,7 @@ class Reservation(NamedCommon, TemplateSchemaMixin):
         active_subs = [x for x in subs if (x.status in [SchedulingUnitBlueprint.Status.OBSERVING.value, SchedulingUnitBlueprint.Status.SCHEDULED.value]
                                        and x.scheduled_on_sky_stop_time >= self.start_time)]
         if self.stop_time:
-            active_subs = [x for x in active_subs if self.scheduled_on_sky_start_time <= self.stop_time]
+            active_subs = [x for x in active_subs if x.scheduled_on_sky_start_time <= self.stop_time]
 
         # Raise an exception if any of these scheduling units uses a station that shall be reserved
         if "resources" in self.specifications_doc and "stations" in self.specifications_doc["resources"]: