diff --git a/src/cat/LegacyLuaAPI.cpp b/src/cat/LegacyLuaAPI.cpp
index cb6fd9af4..3557c6f4a 100644
--- a/src/cat/LegacyLuaAPI.cpp
+++ b/src/cat/LegacyLuaAPI.cpp
@@ -1739,7 +1739,7 @@ int luatpt_message_box(lua_State* l)
 {
 	std::string title = std::string(luaL_optstring(l, 1, "Title"));
 	std::string message = std::string(luaL_optstring(l, 2, "Message"));
-	int large = luaL_optint(l, 3, 0);
+	int large = lua_isboolean(l, 3)?lua_toboolean(l, 3):0;
 	new InformationMessage(title, message, large);
 	return 0;
 }