diff --git a/tagilmo/VereyaPython/agent_host.py b/tagilmo/VereyaPython/agent_host.py
index 8f14815..b909b9a 100644
--- a/tagilmo/VereyaPython/agent_host.py
+++ b/tagilmo/VereyaPython/agent_host.py
@@ -548,7 +548,7 @@ def onMissionControlMessage(self, xml: TimestampedString) -> Optional[None]:
                     return
                 assert self.current_mission_record is not None
                 if self.current_mission_record.isRecording():
-                    missionEndedXML = open(self.current_mission_record.getMissionEndedPath(), 'aw')
+                    missionEndedXML = open(self.current_mission_record.getMissionEndedPath(), 'a')
                     missionEndedXML.write(xml.text)
                     missionEndedXML.close()
                 self.close()