diff --git a/include/boost/beast/websocket/detail/impl_base.hpp b/include/boost/beast/websocket/detail/impl_base.hpp
index e5980bc0..62aa1675 100644
--- a/include/boost/beast/websocket/detail/impl_base.hpp
+++ b/include/boost/beast/websocket/detail/impl_base.hpp
@@ -311,7 +311,7 @@ struct impl_base<true>
     read_size_hint_pmd(
         std::size_t initial_size,
         bool rd_done,
-        std::uint64_t rd_msg_max,
+        std::size_t rd_msg_max,
         std::uint64_t rd_remain,
         frame_header const& rd_fh) const
     {
@@ -465,7 +465,7 @@ struct impl_base<false>
     read_size_hint_pmd(
         std::size_t initial_size,
         bool rd_done,
-        std::uint64_t rd_msg_max,
+        std::size_t rd_msg_max,
         std::uint64_t rd_remain,
         frame_header const& rd_fh) const
     {