diff --git a/lpc_aspeed.hpp b/lpc_aspeed.hpp
index 1c4481a..98e7a72 100644
--- a/lpc_aspeed.hpp
+++ b/lpc_aspeed.hpp
@@ -12,9 +12,9 @@
 {
   public:
     static std::unique_ptr<LpcMapperInterface>
-        createAspeedMapper(size_t regionSize);
+        createAspeedMapper(std::size_t regionSize);
 
-    LpcMapperAspeed(size_t regionSize,
+    LpcMapperAspeed(std::size_t regionSize,
                     const internal::Sys* sys = &internal::sys_impl) :
         regionSize(regionSize),
         sys(sys){};
@@ -23,7 +23,7 @@
         mapWindow(std::uint32_t address, std::uint32_t length) override;
 
   private:
-    size_t regionSize;
+    std::size_t regionSize;
     const internal::Sys* sys;
 };