diff --git a/include/boost/unordered/unordered_flat_map.hpp b/include/boost/unordered/unordered_flat_map.hpp
index bcaa8dce..b1b2528a 100644
--- a/include/boost/unordered/unordered_flat_map.hpp
+++ b/include/boost/unordered/unordered_flat_map.hpp
@@ -67,6 +67,7 @@ namespace boost {
       using key_type = Key;
       using mapped_type = T;
       using value_type = typename map_types::value_type;
+      using init_type = typename map_types::init_type;
       using size_type = std::size_t;
       using difference_type = std::ptrdiff_t;
       using hasher = Hash;
diff --git a/include/boost/unordered/unordered_flat_set.hpp b/include/boost/unordered/unordered_flat_set.hpp
index fde8605c..fae770ee 100644
--- a/include/boost/unordered/unordered_flat_set.hpp
+++ b/include/boost/unordered/unordered_flat_set.hpp
@@ -49,6 +49,7 @@ namespace boost {
     public:
       using key_type = Key;
       using value_type = typename set_types::value_type;
+      using init_type = typename set_types::init_type;
       using size_type = std::size_t;
       using difference_type = std::ptrdiff_t;
       using hasher = Hash;