diff --git a/ag.cc b/ag.cc
index 018ad12..6e7e1fc 100644
--- a/ag.cc
+++ b/ag.cc
@@ -255,7 +255,7 @@ namespace ag
                     double position[3];
                     for (int i = 0; i < 3; i++)
                     {
-                        int type = lua_type(L, i);
+                        int type = lua_type(L, i + 2);
                         if (type == LUA_TNUMBER  || type == LUA_TSTRING)
                         {
                             position[i] = lua_tonumber(L, i + 2);