diff --git a/include/cppcoro/generator.hpp b/include/cppcoro/generator.hpp
index 9448c81..d39d7e7 100644
--- a/include/cppcoro/generator.hpp
+++ b/include/cppcoro/generator.hpp
@@ -10,6 +10,7 @@
 #include <utility>
 #include <exception>
 #include <iterator>
+#include <functional>
 
 namespace cppcoro
 {