diff --git a/src/agenda_culturel/models.py b/src/agenda_culturel/models.py
index c6071c5..2405841 100644
--- a/src/agenda_culturel/models.py
+++ b/src/agenda_culturel/models.py
@@ -1511,9 +1511,12 @@ class Event(models.Model):
                 self.uuids.append(uuid)
 
         # add possible missing sources
-        for source in other.import_sources:
-            if source not in self.import_sources:
-                self.import_sources.append(source)
+        if other.import_sources:
+            if not self.import_sources:
+                self.import_sources = []
+            for source in other.import_sources:
+                if source not in self.import_sources:
+                    self.import_sources.append(source)
 
     # Limitation: the given events should not be considered similar one to another...
     def import_events(events, remove_missing_from_source=None, user_id=None):