diff --git a/app/scodoc/sco_preferences.py b/app/scodoc/sco_preferences.py
index 2935bdb3ad..92b00a67d8 100644
--- a/app/scodoc/sco_preferences.py
+++ b/app/scodoc/sco_preferences.py
@@ -1949,6 +1949,15 @@ class BasePreferences(object):
                     "name": name,
                 },
             )
+            if len(pdb) > 1:
+                # suppress buggy duplicates (may come from corrupted database for ice ages)
+                log(
+                    f"**oups** detected duplicated preference !\n({self.dept_id}, {formsemestre_id}, {name}, {value})"
+                )
+                for obj in pdb[1:]:
+                    self._editor.delete(cnx, obj["id"])
+                pdb = [pdb[0]]
+
             if not pdb:
                 # crée préférence
                 log("create pref sem=%s %s=%s" % (formsemestre_id, name, value))
@@ -1962,10 +1971,8 @@ class BasePreferences(object):
                     },
                 )
                 modif = True
-                log("create pref sem=%s %s=%s" % (formsemestre_id, name, value))
             else:
                 # edit existing value
-
                 existing_value = pdb[0]["value"]  # old stored value
                 if (
                     (existing_value != value)
diff --git a/sco_version.py b/sco_version.py
index b464e1d193..120cecdf35 100644
--- a/sco_version.py
+++ b/sco_version.py
@@ -1,7 +1,7 @@
 # -*- mode: python -*-
 # -*- coding: utf-8 -*-
 
-SCOVERSION = "9.0.55"
+SCOVERSION = "9.0.56"
 
 SCONAME = "ScoDoc"