diff --git a/Engine.cc b/Engine.cc
index 59f7482..066d902 100644
--- a/Engine.cc
+++ b/Engine.cc
@@ -665,12 +665,15 @@ Engine::Object::Object(const Engine::Object & orig)
 Engine::Object::~Object()
 {
     delete m_ode_object;
-    (*m_display_list_refcnt)--;
-    if (*m_display_list_refcnt < 1)
+    if (m_display_list_refcnt != NULL)
     {
-        /* we hold the last reference to the OpenGL display list */
-        delete m_display_list_refcnt;
-        glDeleteLists(m_display_list, 1);
+        (*m_display_list_refcnt)--;
+        if (*m_display_list_refcnt < 1)
+        {
+            /* we hold the last reference to the OpenGL display list */
+            delete m_display_list_refcnt;
+            glDeleteLists(m_display_list, 1);
+        }
     }
 }
 
diff --git a/ag.cc b/ag.cc
index faa1184..6356267 100644
--- a/ag.cc
+++ b/ag.cc
@@ -40,6 +40,18 @@ namespace ag
             { "isKeyDown", isKeyDown },
             { "registerEventHandler", registerEventHandler },
             { "clearEventHandler", clearEventHandler },
+
+            { "createBox", createBox},
+            { "createStaticBox", createStaticBox},
+            { "createSphere", createSphere},
+            { "createStaticSphere", createStaticSphere},
+            { "createPlane", createPlane},
+            { "createStaticPlane", createStaticPlane},
+            { "createCylinder", createCylinder},
+            { "createStaticCylinder", createStaticCylinder},
+            { "createCCylinder", createCCylinder},
+            { "createStaticCCylinder", createStaticCCylinder},
+
             { NULL, NULL }
         };
         luaL_register(L, "ag", functions);