diff --git a/include/asio/ip/basic_resolver_results.hpp b/include/asio/ip/basic_resolver_results.hpp
index 09de785201..4d741fda68 100644
--- a/include/asio/ip/basic_resolver_results.hpp
+++ b/include/asio/ip/basic_resolver_results.hpp
@@ -133,7 +133,7 @@ class basic_resolver_results
       if (address_info->ai_family == ASIO_OS_DEF(AF_INET)
           || address_info->ai_family == ASIO_OS_DEF(AF_INET6))
       {
-        const std::size_t expected_size =
+        const decltype(asio::detail::addrinfo_type::ai_addrlen) expected_size =
           address_info->ai_family == ASIO_OS_DEF(AF_INET)
             ? sizeof(asio::detail::sockaddr_in4_type)
             : sizeof(asio::detail::sockaddr_in6_type);