diff --git a/physical.hpp b/physical.hpp
index c8ef4fd..3d99066 100644
--- a/physical.hpp
+++ b/physical.hpp
@@ -13,10 +13,10 @@
 namespace led
 {
 /** @brief Assert LED by writing 255 */
-constexpr auto ASSERT = 255;
+constexpr unsigned long ASSERT = 255;
 
 /** @brief De-assert by writing "0" */
-constexpr auto DEASSERT = 0;
+constexpr unsigned long DEASSERT = 0;
 
 /** @class Physical
  *  @brief Responsible for applying actions on a particular physical LED