diff --git a/include/boost/unordered/detail/foa/concurrent_table.hpp b/include/boost/unordered/detail/foa/concurrent_table.hpp
index f1519dfc..255b89d7 100644
--- a/include/boost/unordered/detail/foa/concurrent_table.hpp
+++ b/include/boost/unordered/detail/foa/concurrent_table.hpp
@@ -65,7 +65,7 @@ public:
   void unlock()noexcept{for(auto n=N;n>0;)mutexes[--n].unlock();}
 
 private:
-  mutable std::array<Mutex,N> mutexes;
+  std::array<Mutex,N> mutexes;
 };
 
 /* std::shared_lock is C++14 */