diff --git a/lgc.c b/lgc.c
index fb02f015..c11a5280 100644
--- a/lgc.c
+++ b/lgc.c
@@ -1,5 +1,5 @@
 /*
-** $Id$
+** $Id: lgc.c $
 ** Garbage Collector
 ** See Copyright Notice in lua.h
 */
@@ -212,7 +212,7 @@ void luaC_barrierback_ (lua_State *L, GCObject *o) {
   lua_assert(g->gckind != KGC_GEN || (isold(o) && getage(o) != G_TOUCHED1));
   if (getage(o) != G_TOUCHED2)  /* not already in gray list? */
     linkobjgclist(o, g->grayagain);  /* link it in 'grayagain' */
-  black2gray(o);  /* make table gray (again) */
+  black2gray(o);  /* make object gray (again) */
   setage(o, G_TOUCHED1);  /* touched in current cycle */
 }
 
@@ -515,6 +515,19 @@ static lu_mem traversetable (global_State *g, Table *h) {
 }
 
 
+static int traverseudata (global_State *g, Udata *u) {
+  int i;
+  markobjectN(g, u->metatable);  /* mark its metatable */
+  for (i = 0; i < u->nuvalue; i++)
+    markvalue(g, &u->uv[i].uv);
+  if (g->gckind == KGC_GEN) {
+    linkgclist(u, g->grayagain);  /* keep it in some gray list */
+    black2gray(u);
+  }
+  return 1 + u->nuvalue;
+}
+
+
 /*
 ** Check the cache of a prototype, to keep invariants. If the
 ** cache is white, clear it. (A cache should not prevent the
@@ -613,15 +626,6 @@ static int traversethread (global_State *g, lua_State *th) {
 }
 
 
-static int traverseudata (global_State *g, Udata *u) {
-  int i;
-  markobjectN(g, u->metatable);  /* mark its metatable */
-  for (i = 0; i < u->nuvalue; i++)
-    markvalue(g, &u->uv[i].uv);
-  return 1 + u->nuvalue;
-}
-
-
 /*
 ** traverse one gray object, turning it to black (except for threads,
 ** which are always gray).
diff --git a/testes/all.lua b/testes/all.lua
index cfe21603..37796254 100755
--- a/testes/all.lua
+++ b/testes/all.lua
@@ -1,5 +1,5 @@
 #!../lua
--- $Id: all.lua,v 1.100 2018/03/09 14:23:48 roberto Exp $
+-- $Id: all.lua $
 -- See Copyright Notice at the end of this file
 
 
@@ -162,7 +162,7 @@ olddofile('strings.lua')
 olddofile('literals.lua')
 dofile('tpack.lua')
 assert(dofile('attrib.lua') == 27)
-
+dofile('gengc.lua')
 assert(dofile('locals.lua') == 5)
 dofile('constructs.lua')
 dofile('code.lua', true)
diff --git a/testes/gc.lua b/testes/gc.lua
index 9647cd54..05072efd 100644
--- a/testes/gc.lua
+++ b/testes/gc.lua
@@ -1,7 +1,7 @@
--- $Id: gc.lua,v 1.82 2018/03/12 14:19:36 roberto Exp $
+-- $Id: gc.lua $
 -- See Copyright Notice in file all.lua
 
-print('testing garbage collection')
+print('testing incremental garbage collection')
 
 local debug = require"debug"
 
diff --git a/testes/gengc.lua b/testes/gengc.lua
new file mode 100644
index 00000000..36aed806
--- /dev/null
+++ b/testes/gengc.lua
@@ -0,0 +1,83 @@
+-- $Id: gengc.lua $
+-- See Copyright Notice in file all.lua
+
+print('testing generational garbage collection')
+
+local debug = require"debug"
+
+assert(collectgarbage("isrunning"))
+
+collectgarbage()
+
+local oldmode = collectgarbage("generational")
+
+
+-- ensure that table barrier evolves correctly
+do
+  local U = {}
+  -- full collection makes 'U' old
+  collectgarbage()
+  assert(not T or T.gcage(U) == "old")
+
+  -- U refers to a new table, so it becomes 'touched1'
+  U[1] = {x = {234}}
+  assert(not T or (T.gcage(U) == "touched1" and T.gcage(U[1]) == "new"))
+
+  -- both U and the table survive one more collection
+  collectgarbage("step", 0)
+  assert(not T or (T.gcage(U) == "touched2" and T.gcage(U[1]) == "survival"))
+
+  -- both U and the table survive yet another collection
+  -- now everything is old
+  collectgarbage("step", 0)
+  assert(not T or (T.gcage(U) == "old" and T.gcage(U[1]) == "old1"))
+
+  -- data was not corrupted
+  assert(U[1].x[1] == 234)
+end
+
+
+if T == nil then
+  (Message or print)('\n >>> testC not active: \z
+                             skipping some generational tests <<<\n')
+  print 'OK'
+  return
+end
+
+
+-- ensure that userdata barrier evolves correctly
+do
+  local U = T.newuserdata(0, 1)
+  -- full collection makes 'U' old
+  collectgarbage()
+  assert(T.gcage(U) == "old")
+
+  -- U refers to a new table, so it becomes 'touched1'
+  debug.setuservalue(U, {x = {234}})
+  assert(T.gcage(U) == "touched1" and
+         T.gcage(debug.getuservalue(U)) == "new")
+
+  -- both U and the table survive one more collection
+  collectgarbage("step", 0)
+  assert(T.gcage(U) == "touched2" and
+         T.gcage(debug.getuservalue(U)) == "survival")
+
+  -- both U and the table survive yet another collection
+  -- now everything is old
+  collectgarbage("step", 0)
+  assert(T.gcage(U) == "old" and
+         T.gcage(debug.getuservalue(U)) == "old1")
+
+  -- data was not corrupted
+  assert(debug.getuservalue(U).x[1] == 234)
+end
+
+
+
+-- just to make sure
+assert(collectgarbage'isrunning')
+
+collectgarbage(oldmode)
+
+print('OK')
+