diff --git a/library/phx/system.hpp b/library/phx/system.hpp
index d198a79f5750377c473b9708f2f006760789577f..0e0c3fb2761ae7151f461ce13c7c769e594452ae 100644
--- a/library/phx/system.hpp
+++ b/library/phx/system.hpp
@@ -23,8 +23,6 @@
 #ifndef LIBRARY_PHX_SYSTEM_HPP_
 #define LIBRARY_PHX_SYSTEM_HPP_
 
-#include <string>
-
 #include "phx/export.hpp"
 #include "phx/frame_timer.hpp"
 #include "phx/loggable.hpp"
@@ -34,21 +32,13 @@ class Engine;
 
 class PHOENIX_EXPORT System : public Loggable {
  public:
-  System() = delete;
   virtual ~System() = default;
 
   virtual void Prepare() {}
   virtual void Update(const FrameTimer::TimeInfo&) {}
 
-  Engine* GetEngine() const;
-
  protected:
-  explicit System(Engine* engine);
-  System(const System&) = delete;
-  System(System&&) = default;
-
-  System& operator=(const System&) = delete;
-  System& operator=(System&&) = default;
+  friend Engine;
 
   Engine* engine_ = nullptr;
 };