diff --git a/include/jwt/impl/jwt.ipp b/include/jwt/impl/jwt.ipp
index 8e3649b..e5474e3 100644
--- a/include/jwt/impl/jwt.ipp
+++ b/include/jwt/impl/jwt.ipp
@@ -290,7 +290,9 @@ jwt_signature::get_verify_algorithm_impl(const jwt_header& hdr) const noexcept
 
 //
 template <typename First, typename... Rest>
-jwt_object::jwt_object(First&& first, Rest&&... rest)
+jwt_object::jwt_object(
+    std::enable_if_t<detail::meta::is_parameter_concept<First>::value, First>&& first,
+    Rest&&... rest)
 {
   static_assert (detail::meta::is_parameter_concept<First>::value && 
                  detail::meta::are_all_params<Rest...>::value,
diff --git a/include/jwt/jwt.hpp b/include/jwt/jwt.hpp
index 76eacdd..fbb496e 100644
--- a/include/jwt/jwt.hpp
+++ b/include/jwt/jwt.hpp
@@ -889,7 +889,7 @@ public: // 'tors
    * to populate header. Not much useful unless JWE is supported.
    */
   template <typename First, typename... Rest>
-  jwt_object(First&& first, Rest&&... rest);
+  jwt_object(std::enable_if_t<detail::meta::is_parameter_concept<First>::value, First>&& first, Rest&&... rest);
 
 public: // Exposed static APIs
   /**