diff --git a/include/boost/smart_ptr/detail/spinlock_sync.hpp b/include/boost/smart_ptr/detail/spinlock_sync.hpp
index 854cc7e..cbfdd94 100644
--- a/include/boost/smart_ptr/detail/spinlock_sync.hpp
+++ b/include/boost/smart_ptr/detail/spinlock_sync.hpp
@@ -38,7 +38,7 @@ class spinlock
 {
 public:
 
-    int v_;
+    unsigned char v_;
 
 public: