diff --git a/app/scodoc/sco_moduleimpl_inscriptions.py b/app/scodoc/sco_moduleimpl_inscriptions.py
index 101de24d..ecbcc90b 100644
--- a/app/scodoc/sco_moduleimpl_inscriptions.py
+++ b/app/scodoc/sco_moduleimpl_inscriptions.py
@@ -505,7 +505,11 @@ def _list_but_ue_inscriptions(res: NotesTableCompat, read_only: bool = True) ->
     """
     ]
     table_inscr = _table_but_ue_inscriptions(res)
-    ue_ids = set.union(*(set(x.keys()) for x in table_inscr.values()))
+    ue_ids = (
+        set.union(*(set(x.keys()) for x in table_inscr.values()))
+        if table_inscr
+        else set()
+    )
     ues = sorted(
         (UniteEns.query.get(ue_id) for ue_id in ue_ids),
         key=lambda u: (u.numero or 0, u.acronyme),