diff --git a/test/test.lua b/test/test.lua
index 773e799..1886823 100644
--- a/test/test.lua
+++ b/test/test.lua
@@ -196,6 +196,9 @@ test("encode invalid", function()
     { [1000] = "b" },
     { [ function() end ] = 12 },
     { nil, 2, 3, 4 },
+    { x = 10, [1] = 2 },
+    { [1] = "a", [3] = "b" },
+    { x = 10, [4] = 5 },
   }
   for i, v in ipairs(t) do
     local status, res = pcall(json.encode, v)