diff --git a/AKModel/models.py b/AKModel/models.py
index 5fc04ffba0945a3b010f74a259c6743dea549dd6..ae9abca44c05fcbd800bbbca118cc4a9ac445a02 100644
--- a/AKModel/models.py
+++ b/AKModel/models.py
@@ -406,6 +406,11 @@ class Event(models.Model):
             scheduled_slot["timeslot_ids"] = list(map(int, scheduled_slot["timeslot_ids"]))
             slot = AKSlot.objects.get(id=int(scheduled_slot["ak_id"]))
 
+            if not scheduled_slot["timeslot_ids"]:
+                raise ValueError(
+                    _("AK {ak_name} is not assigned any timeslot by the solver").format(ak_name=slot.ak.name)
+                )
+
             start_timeslot = timeslot_dict[min(scheduled_slot["timeslot_ids"])].avail
             end_timeslot = timeslot_dict[max(scheduled_slot["timeslot_ids"])].avail
             solver_duration = (end_timeslot.end - start_timeslot.start).total_seconds() / 3600.0
@@ -422,10 +427,35 @@ class Event(models.Model):
                     )
                 )
 
-            slot.room = Room.objects.get(id=int(scheduled_slot["room_id"]))
-            slot.start = start_timeslot.start
-            slot.save()
-            slots_updated += 1
+            if slot.fixed:
+                solver_room = Room.objects.get(id=int(scheduled_slot["room_id"]))
+                if slot.room != solver_room:
+                    raise ValueError(
+                        _(
+                            "Fixed AK {ak_name} assigned by solver to room {solver_room} "
+                            "is fixed to room {slot_room}"
+                        ).format(
+                            ak_name=slot.ak.name,
+                            solver_room=solver_room.name,
+                            slot_room=slot.room.name,
+                        )
+                    )
+                if slot.start != start_timeslot.start:
+                    raise ValueError(
+                        _(
+                            "Fixed AK {ak_name} assigned by solver to start at {solver_start} "
+                            "is fixed to start at {slot_start}"
+                        ).format(
+                            ak_name=slot.ak.name,
+                            solver_start=start_timeslot.start,
+                            slot_start=slot.start,
+                        )
+                    )
+            else:
+                slot.room = Room.objects.get(id=int(scheduled_slot["room_id"]))
+                slot.start = start_timeslot.start
+                slot.save()
+                slots_updated += 1
 
         return slots_updated