--- window.cc_org	2022-06-15 11:18:57.176710590 +0200
+++ window.cc	2022-06-15 11:20:06.598793545 +0200
@@ -72,6 +72,7 @@
 #include <sstream>
 #include <algorithm>
 #include <functional>
+#include <optional>
 #include <unordered_map>
 
 Buffer::Buffer(Size const size, Cell const& cell) {