diff --git a/include/boost/unordered/unordered_flat_map.hpp b/include/boost/unordered/unordered_flat_map.hpp
index f65ef252..ce09af90 100644
--- a/include/boost/unordered/unordered_flat_map.hpp
+++ b/include/boost/unordered/unordered_flat_map.hpp
@@ -480,13 +480,13 @@ namespace boost {
         return table_.find(key);
       }
 
-      bool contains(key_type const& key) const
+      BOOST_FORCEINLINE bool contains(key_type const& key) const
       {
         return this->find(key) != this->end();
       }
 
       template <class K>
-      typename std::enable_if<
+      BOOST_FORCEINLINE typename std::enable_if<
         boost::unordered::detail::are_transparent<K, hasher, key_equal>::value,
         bool>::type
       contains(K const& key) const
diff --git a/include/boost/unordered/unordered_flat_set.hpp b/include/boost/unordered/unordered_flat_set.hpp
index 83dddc7f..29c53596 100644
--- a/include/boost/unordered/unordered_flat_set.hpp
+++ b/include/boost/unordered/unordered_flat_set.hpp
@@ -356,13 +356,13 @@ namespace boost {
         return table_.find(key);
       }
 
-      bool contains(key_type const& key) const
+      BOOST_FORCEINLINE bool contains(key_type const& key) const
       {
         return this->find(key) != this->end();
       }
 
       template <class K>
-      typename std::enable_if<
+      BOOST_FORCEINLINE typename std::enable_if<
         boost::unordered::detail::are_transparent<K, hasher, key_equal>::value,
         bool>::type
       contains(K const& key) const