diff --git a/lref.c b/lref.c
index 2479141c..5c22b63b 100644
--- a/lref.c
+++ b/lref.c
@@ -1,5 +1,5 @@
 /*
-** $Id: $
+** $Id: lref.c,v 1.1 1999/10/04 17:50:24 roberto Exp roberto $
 ** REF mechanism
 ** See Copyright Notice in lua.h
 */
@@ -16,31 +16,36 @@ int luaR_ref (const TObject *o, int lock) {
   if (ttype(o) == LUA_T_NIL)
     ref = LUA_REFNIL;
   else {
-    for (ref=0; ref<L->refSize; ref++)
-      if (L->refArray[ref].status == FREE)
-        break;
-    if (ref == L->refSize) {  /* no more empty spaces? */
+    if (L->refFree != NONEXT) {  /* is there a free place? */
+      ref = L->refFree;
+      L->refFree = L->refArray[ref].st;
+    }
+    else {  /* no more free places */
       luaM_growvector(L->refArray, L->refSize, 1, struct ref, refEM, MAX_INT);
-      L->refSize++;
+      ref = L->refSize++;
     }
     L->refArray[ref].o = *o;
-    L->refArray[ref].status = lock ? LOCK : HOLD;
+    L->refArray[ref].st = lock ? LOCK : HOLD;
   }
   return ref;
 }
 
 
 void lua_unref (int ref) {
-  if (ref >= 0 && ref < L->refSize)
-    L->refArray[ref].status = FREE;
+  if (ref >= 0) {
+    if (ref >= L->refSize || L->refArray[ref].st >= 0)
+      lua_error("API error - invalid parameter for function `lua_unref'");
+    L->refArray[ref].st = L->refFree;
+    L->refFree = ref;
+  }
 }
 
 
 const TObject *luaR_getref (int ref) {
   if (ref == LUA_REFNIL)
     return &luaO_nilobject;
-  if (ref >= 0 && ref < L->refSize &&
-      (L->refArray[ref].status == LOCK || L->refArray[ref].status == HOLD))
+  else if (0 <= ref && ref < L->refSize &&
+          (L->refArray[ref].st == LOCK || L->refArray[ref].st == HOLD))
     return &L->refArray[ref].o;
   else
     return NULL;
@@ -63,16 +68,28 @@ static int ismarked (const TObject *o) {
     case LUA_T_CMARK: case LUA_T_PMARK:
       LUA_INTERNALERROR("invalid type");
 #endif
-    default:  /* nil, number or cproto */
+    default:  /* number or cproto */
       return 1;
   }
 }
 
 
+/* for internal debugging only; check if a link of free refs is valid */
+#define VALIDLINK(st,n)	(NONEXT <= (st) && (st) < (n))
+
 void luaR_invalidaterefs (void) {
+  int n = L->refSize;
   int i;
-  for (i=0; i<L->refSize; i++)
-    if (L->refArray[i].status == HOLD && !ismarked(&L->refArray[i].o))
-      L->refArray[i].status = COLLECTED;
+  for (i=0; i<n; i++) {
+    struct ref *r = &L->refArray[i];
+    if (r->st == HOLD && !ismarked(&r->o))
+      r->st = COLLECTED;
+    LUA_ASSERT((r->st == LOCK && ismarked(&r->o)) ||
+                r->st == COLLECTED ||
+                r->st == NONEXT ||
+               (r->st < n && VALIDLINK(L->refArray[r->st].st, n)),
+               "inconsistent ref table");
+  }
+  LUA_ASSERT(VALIDLINK(L->refFree, n), "inconsistent ref table");
 }
 
diff --git a/lref.h b/lref.h
index 60e14e85..180daab0 100644
--- a/lref.h
+++ b/lref.h
@@ -1,5 +1,5 @@
 /*
-** $Id: $
+** $Id: lref.h,v 1.1 1999/10/04 17:50:24 roberto Exp roberto $
 ** REF mechanism
 ** See Copyright Notice in lua.h
 */
@@ -9,6 +9,19 @@
 
 #include "lobject.h"
 
+
+#define NONEXT          -1      /* to end the free list */
+#define HOLD            -2
+#define COLLECTED       -3
+#define LOCK            -4
+
+
+struct ref {
+  TObject o;
+  int st;  /* can be LOCK, HOLD, COLLECTED, or next (for free list) */
+};
+
+
 int luaR_ref (const TObject *o, int lock);
 const TObject *luaR_getref (int ref);
 void luaR_invalidaterefs (void);