diff --git a/ag.cc b/ag.cc
index 3f6f7b0..52990e7 100644
--- a/ag.cc
+++ b/ag.cc
@@ -29,6 +29,7 @@ namespace ag
             { "endFrame", endFrame },
             { "setCamera", setCamera },
             { "elapsedTime", elapsedTime },
+            { "doPhysics", doPhysics },
             { NULL, NULL }
         };
         luaL_register(L, "ag", functions);
diff --git a/anaglym.cc b/anaglym.cc
index 4da1353..6997bba 100644
--- a/anaglym.cc
+++ b/anaglym.cc
@@ -303,10 +303,14 @@ void Engine::update()
     lua_getfield(m_luaState, LUA_GLOBALSINDEX, "update");
     if (lua_type(m_luaState, -1) == LUA_TFUNCTION)
     {
-        int s = lua_pcall(m_luaState, 0, 0, 0);
+        /* call the update function - pops the function ref from the stack */
+        int s = lua_pcall(m_luaState, 0, LUA_MULTRET, 0);
         reportErrors(s);
     }
-    lua_pop(m_luaState, 1);
+    else
+    {
+        lua_pop(m_luaState, 1);
+    }
     m_drawing = false;
 }