diff --git a/src/agenda_culturel/models.py b/src/agenda_culturel/models.py
index ee9ba72..194d36a 100644
--- a/src/agenda_culturel/models.py
+++ b/src/agenda_culturel/models.py
@@ -251,7 +251,8 @@ class Event(models.Model):
             self.created_date = now
         if hasattr(self, "require_imported_date"):
             self.imported_date = now
-        self.modified_date = now
+        if not hasattr(self, "require_imported_date") or self.modified_date is None:
+            self.modified_date = now
 
 
     def prepare_save(self):
@@ -294,10 +295,10 @@ class Event(models.Model):
             del event_structure["url_human"]
 
         if "last_modified" in event_structure and event_structure["last_modified"] is not None:
-            event_structure["created_date"] = event_structure["last_modified"]
+            event_structure["modified_date"] = event_structure["last_modified"]
             del event_structure["last_modified"]
         else:
-            event_structure["created_date"] = timezone.now()
+            event_structure["created_date"] = None
 
         if "start_time" in event_structure:
             event_structure["start_time"] = time.fromisoformat(event_structure["start_time"])