diff --git a/include/boost/hana/functional.hpp b/include/boost/hana/functional.hpp
index 57f2a073a..71664ffdd 100644
--- a/include/boost/hana/functional.hpp
+++ b/include/boost/hana/functional.hpp
@@ -13,8 +13,6 @@ Distributed under the Boost Software License, Version 1.0.
 #include <boost/hana/detail/at_index/best.hpp>
 #include <boost/hana/detail/constexpr.hpp>
 
-#include <cstddef>
-
 
 namespace boost { namespace hana {
     namespace functional_detail {
@@ -71,7 +69,7 @@ namespace boost { namespace hana {
     //! Maybe this should be `arg(n)` instead of `arg<n>`? It's more
     //! consistent but harder to use since we have to write `arg(int_<n>)(...)`
     //! instead of `arg<n>(...)`.
-    template <std::size_t n>
+    template <decltype(sizeof(int)) n>
     BOOST_HANA_CONSTEXPR_LAMBDA auto arg = [](auto ...xs) {
         static_assert(n > 0,
         "invalid usage of arg with n == 0");
diff --git a/include/boost/hana/integral.hpp b/include/boost/hana/integral.hpp
index 4274e24d5..7c765c565 100644
--- a/include/boost/hana/integral.hpp
+++ b/include/boost/hana/integral.hpp
@@ -15,7 +15,6 @@ Distributed under the Boost Software License, Version 1.0.
 #include <boost/hana/logical/mcd.hpp>
 #include <boost/hana/orderable/less_mcd.hpp>
 
-#include <cstddef>
 #include <type_traits>
 
 
@@ -115,10 +114,10 @@ namespace boost { namespace hana {
         constexpr int to_int(char c)
         { return static_cast<int>(c) - 48; }
 
-        template <std::size_t N>
+        template <decltype(sizeof(int)) N>
         constexpr long long parse(const char (&arr)[N]) {
             long long number = 0, base = 1;
-            for (std::size_t i = 0; i < N; ++i) {
+            for (decltype(N) i = 0; i < N; ++i) {
                 number += to_int(arr[N - 1 - i]) * base;
                 base *= 10;
             }