diff --git a/rtb/core/ad_selector.hpp b/rtb/core/ad_selector.hpp
index 52747f5..8055858 100644
--- a/rtb/core/ad_selector.hpp
+++ b/rtb/core/ad_selector.hpp
@@ -52,6 +52,7 @@ static auto chain_function(BidRequest &&req, Impression &&imp, Arg &&arg,
 
 } // namespace detail
 
+// TODO: move to concepts
 template <typename T>
 concept is_vanilla_standard_ad = requires(T value) {
     value.auth_bid_micros;