diff --git a/frontend/document/koptinterface.lua b/frontend/document/koptinterface.lua
index 7ffbbda4c..4f5e10113 100644
--- a/frontend/document/koptinterface.lua
+++ b/frontend/document/koptinterface.lua
@@ -263,7 +263,7 @@ function KoptInterface:getCoverPageImage(doc)
     local zoom = math.min(screen_size.w / native_size.w, screen_size.h / native_size.h)
     local tile = Document.renderPage(doc, 1, nil, zoom, 0, 1, 0)
     if tile then
-        return tile.bb
+        return tile.bb:copy()
     end
 end