diff --git a/backend/app/dav/caldav.py b/backend/app/dav/caldav.py
index 7ba0de9..e79d185 100644
--- a/backend/app/dav/caldav.py
+++ b/backend/app/dav/caldav.py
@@ -333,6 +333,11 @@ def report(subpath):
     multistatus = ET.Element(_qn('d', 'multistatus'))
     tag = root.tag
 
+    # Prüfen ob der Client calendar-data angefragt hat. Falls nicht,
+    # liefern wir es auch nicht mit - strikter nach RFC und DAVx5
+    # entscheidet dann sauber "ich brauche Phase 2: multiget".
+    wants_data = root.find(f".//{_qn('c', 'calendar-data')}") is not None
+
     if tag == _qn('c', 'calendar-multiget'):
         hrefs = [h.text for h in root.findall(_qn('d', 'href')) if h.text]
         for href in hrefs:
@@ -343,8 +348,6 @@ def report(subpath):
         return _xml_response(multistatus)
 
     if tag == _qn('c', 'calendar-query'):
-        # Parse optional time-range. start ohne end = "ab jetzt offen";
-        # end ohne start = "bis X"; beide None = kein Filter.
         start, end = _extract_time_range(root)
         q = CalendarEvent.query.filter_by(calendar_id=cal.id)
         if end is not None:
@@ -355,7 +358,7 @@ def report(subpath):
                 | (CalendarEvent.recurrence_rule.isnot(None))
             )
         for ev in q.all():
-            multistatus.append(_event_response(user, cal, ev, include_data=True))
+            multistatus.append(_event_response(user, cal, ev, include_data=wants_data))
         return _xml_response(multistatus)
 
     # Unknown report - return empty multistatus so clients don't break