diff --git a/libs/bt/include/psemek/bt/action.hpp b/libs/bt/include/psemek/bt/action.hpp
index 7cf6dedb..ff105bb3 100644
--- a/libs/bt/include/psemek/bt/action.hpp
+++ b/libs/bt/include/psemek/bt/action.hpp
@@ -2,8 +2,6 @@
 
 #include <psemek/bt/node.hpp>
 
-#include <optional>
-
 namespace psemek::bt
 {
 
@@ -19,6 +17,8 @@ namespace psemek::bt
 		using typename node_type::finished;
 		using typename node_type::status;
 
+		static_assert(std::is_same_v<std::result_of_t<ActionFn(Time, Args...)>, void>, "bt::action result type must be void");
+
 		action_node(ActionFn && action_fn)
 			: action_fn_(std::move(action_fn))
 		{}