diff --git a/CHANGELOG.md b/CHANGELOG.md
index a80f71d5..cfeae521 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 Version 163:
 
 * Tidy up calls to post()
+* Fix narrowing warnings
 
 --------------------------------------------------------------------------------
 
diff --git a/include/boost/beast/websocket/detail/mask.hpp b/include/boost/beast/websocket/detail/mask.hpp
index ff4115b0..651b6328 100644
--- a/include/boost/beast/websocket/detail/mask.hpp
+++ b/include/boost/beast/websocket/detail/mask.hpp
@@ -98,7 +98,7 @@ prepare_key(prepared_key& prepared, std::uint32_t key)
 
 template<std::size_t N>
 void
-rol(std::array<unsigned char, N>& v, unsigned n)
+rol(std::array<unsigned char, N>& v, std::size_t n)
 {
     auto v0 = v;
     for(std::size_t i = 0; i < v.size(); ++i )