diff --git a/docgen/util.lua b/docgen/util.lua
index 202712c..97e2fb0 100644
--- a/docgen/util.lua
+++ b/docgen/util.lua
@@ -49,7 +49,7 @@ end
 
 M.filter = function(list, pred)
     local ret = {}
-    if type(list) == "table" then
+    if type(list) == "table" and getmetatable(list) == nil then
         for i, v in ipairs(list) do
             if pred(v) then
                 ret[#ret + 1] = v