diff --git a/include/boost/unordered/detail/foa.hpp b/include/boost/unordered/detail/foa.hpp
index 4310e0e7..bd248b03 100644
--- a/include/boost/unordered/detail/foa.hpp
+++ b/include/boost/unordered/detail/foa.hpp
@@ -1306,7 +1306,7 @@ private:
   }
 
   template<typename Key>
-  inline std::size_t hash_for(const Key& x)
+  inline std::size_t hash_for(const Key& x)const
   {
     return mix_policy::mix(h()(x));
   }