diff --git a/sat/memory/sqla_mapping.py b/sat/memory/sqla_mapping.py
index 8c1e91c8..377e4948 100644
--- a/sat/memory/sqla_mapping.py
+++ b/sat/memory/sqla_mapping.py
@@ -273,7 +273,7 @@ class History(Base):
         return f"History<{self.source_jid.full()}->{self.dest_jid.full()} [{dt}]>"
 
     def serialise(self):
-        extra = self.extra
+        extra = self.extra or {}
         if self.origin_id is not None:
             extra["origin_id"] = self.origin_id
         if self.stanza_id is not None: