diff --git a/oop/oop.lua b/oop/oop.lua
index f28a6a3..ef024f6 100644
--- a/oop/oop.lua
+++ b/oop/oop.lua
@@ -34,6 +34,38 @@ end
 local function_def_cache = setmetatable({}, { __mode = "k" })
 oop._call_stack = {}
 
+local default_dunders = {
+    "__add",
+    "__sub",
+    "__mul",
+    "__div",
+    "__idiv",
+    "__mod",
+    "__pow",
+    "__unm",
+    "__band",
+    "__bor",
+    "__bxor",
+    "__bnot",
+    "__shl",
+    "__shr",
+    "__concat",
+    "__len",
+    "__eq",
+    "__lt",
+    "__le",
+    "__pairs",
+    "__ipairs",
+    "__call",
+    "__tostring"
+}
+
+local function deny_op(name)
+    return function()
+        error("operation not allowed: " .. name, 2)
+    end
+end
+
 local function normalize_visibility(visibility)
     if visibility == nil then
         return oop.Visibility.PUBLIC
@@ -263,6 +295,12 @@ function oop.class(def, base)
         end
     })
 
+    for _, name in ipairs(default_dunders) do
+        if rawget(cls, name) == nil then
+            cls[name] = deny_op(name)
+        end
+    end
+
     if type(def) == "string" then
         cls.__name = def
     elseif type(def) == "function" then