diff --git a/luprex/core/cpp/gui.cpp b/luprex/core/cpp/gui.cpp
index 44fb88a4..92ccea56 100644
--- a/luprex/core/cpp/gui.cpp
+++ b/luprex/core/cpp/gui.cpp
@@ -10,6 +10,15 @@ void Gui::menu_item(const std::string &action, const std::string &label) {
     elts_.push_back(elt);
 }
 
+bool Gui::has_action(const std::string &action) const {
+    for (const GuiElt &elt : elts_) {
+        if (elt.action_ == action) {
+            return true;
+        }
+    }
+    return false;
+}
+
 LuaDefine(gui_create, "c") {
     LuaRet lgui;
     LuaStack LS(L, lgui);
diff --git a/luprex/core/cpp/gui.hpp b/luprex/core/cpp/gui.hpp
index 1860971c..e1452a80 100644
--- a/luprex/core/cpp/gui.hpp
+++ b/luprex/core/cpp/gui.hpp
@@ -32,6 +32,7 @@ private:
 public:
     const EltVec &elts() const { return elts_; }
     void clear() { elts_.clear(); }
+    bool has_action(const std::string &action) const;
     void menu_item(const std::string &action, const std::string &label);
 };
 
diff --git a/luprex/core/cpp/world.cpp b/luprex/core/cpp/world.cpp
index 4d9543ac..2de05651 100644
--- a/luprex/core/cpp/world.cpp
+++ b/luprex/core/cpp/world.cpp
@@ -193,6 +193,13 @@ void World::update_gui(int64_t actor_id, int64_t place_id, Gui *gui) {
 }
 
 void World::invoke_plan(int64_t actor_id, int64_t place_id, const std::string &action, Gui *gui) {
+    // Validate that the action is legal.
+    Gui validation_gui;
+    update_gui(actor_id, place_id, &validation_gui);
+    if (!validation_gui.has_action(action)) {
+        return;
+    }
+
     lua_State *L = state();
 
     LuaVar actor, place, ugui, func, tangibles, mt, index, actions;