diff --git a/sync/spinlock.h b/sync/spinlock.h
index ba73e41..a3f8941 100644
--- a/sync/spinlock.h
+++ b/sync/spinlock.h
@@ -35,14 +35,15 @@ class Spinlock {
   // Prevent copies and assignments
   Spinlock(const Spinlock& copy) = delete;
   Spinlock& operator=(const Spinlock&) = delete;
-
+ private:
+  volatile uint64_t locked;
  public:
   /*! \brief Constructor; Initializes as unlocked.
    *
    *  \todo(12) Complete Constructor (for \MPStuBS, or use \ref Ticketlock)
    *
    */
-  consteval Spinlock() {}
+  consteval Spinlock() : locked(0) {}
 
   /*! \brief Enters the critical area. In case the area is already locked,
    *  \ref lock() will actively wait until the area can be entered.
@@ -50,11 +51,11 @@ class Spinlock {
    *  \see \ref Core::pause()
    *  \todo(12) Implement Method (for \MPStuBS, or use \ref Ticketlock)
    */
-  void lock() {}
+  void lock();
 
   /*! \brief Unblocks the critical area.
    *
    *  \todo(12) Implement Method (for \MPStuBS, or use \ref Ticketlock)
    */
-  void unlock() {}
+  void unlock();
 };