diff --git a/include/boost/mp11/detail/mp_for_index.hpp b/include/boost/mp11/detail/mp_for_index.hpp
index 88a3293..8ae5aac 100644
--- a/include/boost/mp11/detail/mp_for_index.hpp
+++ b/include/boost/mp11/detail/mp_for_index.hpp
@@ -62,7 +62,7 @@ template<> struct mp_for_index_impl_<0>
 
 template<> struct mp_for_index_impl_<1>
 {
-    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t /*i*/, F && f )
     {
         return std::forward<F>(f)( mp_size_t<K+0>() );
     }
diff --git a/include/boost/mp11_single.hpp b/include/boost/mp11_single.hpp
index 277c0a2..a27cc0e 100644
--- a/include/boost/mp11_single.hpp
+++ b/include/boost/mp11_single.hpp
@@ -1163,7 +1163,7 @@ template<> struct mp_for_index_impl_<0>
 
 template<> struct mp_for_index_impl_<1>
 {
-    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t /*i*/, F && f )
     {
         return std::forward<F>(f)( mp_size_t<K+0>() );
     }