diff --git a/lib/kolab_sync_data_calendar.php b/lib/kolab_sync_data_calendar.php
--- a/lib/kolab_sync_data_calendar.php
+++ b/lib/kolab_sync_data_calendar.php
@@ -803,13 +803,21 @@
             throw new Syncroton_Exception_Status_MeetingResponse(Syncroton_Exception_Status_MeetingResponse::INVALID_REQUEST);
         }
 
-        if ($event['free_busy']) {
-            $old['free_busy'] = $event['free_busy'];
+        // Update event properties
+        // FIXME: Can we be smarter here? Should we update everything? What about e.g. new attendees?
+        if (isset($event['sequence']) && $event['sequence'] > $old['sequence']) {
+            $props = ['start', 'end', 'title', 'description', 'location', 'free_busy', 'sequence'];
+            foreach ($props as $prop) {
+                if (isset($event[$prop])) {
+                    $old[$prop] = $event[$prop];
+                }
+            }
+        }
+        else {
+            // Updating an existing event is most-likely a response
+            // to an iTip request with bumped SEQUENCE
+            $old['sequence'] += 1;
         }
-
-        // Updating an existing event is most-likely a response
-        // to an iTip request with bumped SEQUENCE
-        $old['sequence'] += 1;
 
         // Copy new custom properties
         if (!empty($event['x-custom'])) {