diff --git a/include/boost/openmethod/policies/minimal_perfect_hash.hpp b/include/boost/openmethod/policies/minimal_perfect_hash.hpp
index ef0082c..a32b60c 100644
--- a/include/boost/openmethod/policies/minimal_perfect_hash.hpp
+++ b/include/boost/openmethod/policies/minimal_perfect_hash.hpp
@@ -17,6 +17,21 @@
 #pragma warning(disable : 4702) // unreachable code
 #endif
 
+namespace boost::openmethod::detail {
+
+#if defined(UINTPTR_MAX)
+using uintptr = std::uintptr_t;
+constexpr uintptr uintptr_max = UINTPTR_MAX;
+#else
+static_assert(
+    sizeof(std::size_t) == sizeof(void*),
+    "This implementation requires that size_t and void* have the same size.");
+using uintptr = std::size_t;
+constexpr uintptr uintptr_max = (std::numeric_limits<std::size_t>::max)();
+#endif
+
+} // namespace boost::openmethod::detail
+
 namespace boost::openmethod {
 
 namespace detail {