diff --git a/Function.hpp b/Function.hpp
index 92cbe23..1197f01 100644
--- a/Function.hpp
+++ b/Function.hpp
@@ -14,7 +14,7 @@ private:
     class callable_base
     {
     public:
-        virtual Ret call(Args...) = 0;
+        virtual Ret call(Args...) const = 0;
         virtual ~callable_base() {}
         //virtual ~callable_base() = default;    // melyik számít szebbnek? van bármi különbség?
     };
@@ -27,7 +27,7 @@ private:
     public:
         callable(Fun fun):_fun(fun) {}
 
-        virtual Ret call(Args... args) override
+        virtual Ret call(Args... args) const override
         { return _fun(std::forward<Args>(args)...); }
 
         virtual ~callable() override {}