diff --git a/common/luaobject.h b/common/luaobject.h
index 19aca17f..056368bd 100644
--- a/common/luaobject.h
+++ b/common/luaobject.h
@@ -106,6 +106,20 @@ luaA_object_ref(lua_State *L, int oud)
     return p;
 }
 
+/** Reference an object and return a pointer to it checking its type.
+ * That only works with userdata.
+ * \param L The Lua VM state.
+ * \param oud The object index on the stack.
+ * \param class The class of object expected
+ * \return The object reference, or NULL if not referenceable.
+ */
+static inline void *
+luaA_object_ref_class(lua_State *L, int oud, lua_class_t *class)
+{
+    luaA_checkudata(L, oud, class);
+    return luaA_object_ref(L, oud);
+}
+
 /** Unreference an object and return a pointer to it.
  * That only works with userdata, table, thread or function.
  * \param L The Lua VM state.
diff --git a/root.c b/root.c
index b91067a2..f9540ef5 100644
--- a/root.c
+++ b/root.c
@@ -126,7 +126,7 @@ luaA_root_keys(lua_State *L)
 
         lua_pushnil(L);
         while(lua_next(L, 1))
-            key_array_append(&globalconf.keys, luaA_object_ref(L, -1));
+            key_array_append(&globalconf.keys, luaA_object_ref_class(L, -1, &key_class));
 
         int nscreen = xcb_setup_roots_length(xcb_get_setup(globalconf.connection));
 
diff --git a/tag.c b/tag.c
index dfb5365e..31357f90 100644
--- a/tag.c
+++ b/tag.c
@@ -127,7 +127,7 @@ tag_append_to_screen(lua_State *L, int udx, screen_t *s)
     int phys_screen = screen_virttophys(screen_index);
 
     tag->screen = s;
-    tag_array_append(&s->tags, luaA_object_ref(globalconf.L, udx));
+    tag_array_append(&s->tags, luaA_object_ref_class(globalconf.L, udx, &tag_class));
     ewmh_update_net_numbers_of_desktop(phys_screen);
     ewmh_update_net_desktop_names(phys_screen);
     ewmh_update_workarea(phys_screen);
@@ -210,7 +210,7 @@ tag_client_emit_signal(lua_State *L, tag_t *t, client_t *c, const char *signame)
 void
 tag_client(client_t *c)
 {
-    tag_t *t = luaA_object_ref(globalconf.L, -1);
+    tag_t *t = luaA_object_ref_class(globalconf.L, -1, &tag_class);
 
     /* don't tag twice */
     if(is_client_tagged(c, t))
diff --git a/titlebar.c b/titlebar.c
index 2a363308..9d73efe3 100644
--- a/titlebar.c
+++ b/titlebar.c
@@ -224,7 +224,7 @@ void
 titlebar_client_attach(client_t *c)
 {
     /* check if we can register the object */
-    wibox_t *t = luaA_object_ref(globalconf.L, -1);
+    wibox_t *t = luaA_object_ref_class(globalconf.L, -1, &wibox_class);
 
     titlebar_client_detach(c);
 
diff --git a/wibox.c b/wibox.c
index 3c51f664..feb8403d 100644
--- a/wibox.c
+++ b/wibox.c
@@ -738,7 +738,7 @@ wibox_attach(lua_State *L, int udx, screen_t *s)
     /* duplicate wibox */
     lua_pushvalue(L, udx);
     /* ref it */
-    wibox_t *wibox = luaA_object_ref(globalconf.L, -1);
+    wibox_t *wibox = luaA_object_ref_class(globalconf.L, -1, &wibox_class);
 
     wibox_detach(L, udx);