Index: uspace/lib/cpp/include/impl/ios.hpp
===================================================================
--- uspace/lib/cpp/include/impl/ios.hpp	(revision c729a60b4f499d18d9755e92e7587ac632b7fd47)
+++ uspace/lib/cpp/include/impl/ios.hpp	(revision 573264848ed905f3d2877fd9cc0ff835815fa9f1)
@@ -214,4 +214,11 @@
 
             vector<pair<event_callback, int>> callbacks_;
+
+        private:
+            static constexpr size_t buffer_size_{64};
+            char buffer_[buffer_size_];
+
+            template<class Char, class Iterator>
+            friend class num_put;
     };