diff --git a/plugins/calibre.koplugin/metadata.lua b/plugins/calibre.koplugin/metadata.lua
index 518aef84e..0cf9fe4d6 100644
--- a/plugins/calibre.koplugin/metadata.lua
+++ b/plugins/calibre.koplugin/metadata.lua
@@ -39,12 +39,12 @@ local search_used_metadata = {
 }
 
 local function slim(book, is_search)
-    local slim_book = {}
+    local slim_book = rapidjson.object({})
     for _, k in ipairs(is_search and search_used_metadata or used_metadata) do
         if k == "series" or k == "series_index" then
             slim_book[k] = book[k] or rapidjson.null
         elseif k == "tags" or k == "authors" then
-            slim_book[k] = book[k] or {}
+            slim_book[k] = book[k] or rapidjson.array({})
         else
             slim_book[k] = book[k]
         end