diff --git a/plugins/kosync.koplugin/main.lua b/plugins/kosync.koplugin/main.lua
index 29aa888ab..1234b7fb9 100644
--- a/plugins/kosync.koplugin/main.lua
+++ b/plugins/kosync.koplugin/main.lua
@@ -605,6 +605,7 @@ function KOSync:_onResume()
 end
 
 function KOSync:_onFlushSettings()
+    if self.ui == nil or self.ui.document == nil then return end
     self:updateProgress()
 end