diff --git a/string.hpp b/string.hpp
index 18e5cf19..78b61805 100644
--- a/string.hpp
+++ b/string.hpp
@@ -350,6 +350,8 @@ namespace cruft::string {
             return false;
         }
 
+        using is_transparent = void;
+
         template <typename A, typename B>
         requires (!std::is_same_v<A,B>)
         bool operator() (A &&a, B &&b) const noexcept