diff --git a/aleksis/apps/untis/util/mysql/importers/substitutions.py b/aleksis/apps/untis/util/mysql/importers/substitutions.py
index cea7a5d3b4074f0a23f80bffda1d23122d34b938..3f5d51017cd9f58d36cc8c3ef71e70ced30b6e50 100644
--- a/aleksis/apps/untis/util/mysql/importers/substitutions.py
+++ b/aleksis/apps/untis/util/mysql/importers/substitutions.py
@@ -236,7 +236,7 @@ def import_substitutions(
 
                 # Supervision
                 area_ref = supervision_areas_ref[sub.corridor_id]
-                possible_supervisions = area_ref["supervisions"][weekday][period]
+                possible_supervisions = area_ref["supervisions"].get(weekday, {}).get(period, [])
 
                 supervision = None
                 for possible_supervision in possible_supervisions: