diff --git a/include/CLI/FormatterFwd.hpp b/include/CLI/FormatterFwd.hpp
index f71b3bba4..dee6c5a5f 100644
--- a/include/CLI/FormatterFwd.hpp
+++ b/include/CLI/FormatterFwd.hpp
@@ -7,6 +7,7 @@
 #pragma once
 
 // [CLI11:public_includes:set]
+#include <functional>
 #include <map>
 #include <string>
 #include <utility>