diff --git a/OPTYap/tab.insts.i b/OPTYap/tab.insts.i
index e8e727655..1ce06fd17 100644
--- a/OPTYap/tab.insts.i
+++ b/OPTYap/tab.insts.i
@@ -1110,20 +1110,22 @@
     if (TrNode_child(ans_node)) {
       /* unconsumed answers */
 #ifdef MODE_DIRECTED_TABLING
-      ans_node_ptr first_ans_node, aux_ans_node;
-      first_ans_node = ans_node;
-      do {
+      if (IS_INVALID_LEAF_NODE(TrNode_child(ans_node))) {
+	ans_node_ptr first_ans_node, aux_ans_node;
+	first_ans_node = ans_node;
 	ans_node = TrNode_child(ans_node);
-      } while (IS_INVALID_LEAF_NODE(ans_node));
-      aux_ans_node = TrNode_child(first_ans_node);
-      while (aux_ans_node != ans_node) {
-	TrNode_child(first_ans_node) = ans_node;
-	first_ans_node = aux_ans_node;
-        aux_ans_node = TrNode_child(first_ans_node);
-      }
-#else
-      ans_node = TrNode_child(ans_node);
+	do {
+	  ans_node = TrNode_child(ans_node);
+	} while (IS_INVALID_LEAF_NODE(ans_node));
+	aux_ans_node = TrNode_child(first_ans_node);
+        do {
+	  TrNode_child(first_ans_node) = ans_node;
+	  first_ans_node = aux_ans_node;
+	  aux_ans_node = TrNode_child(first_ans_node);
+	} while (aux_ans_node != ans_node);
+      } else
 #endif /* MODE_DIRECTED_TABLING */
+	ans_node = TrNode_child(ans_node);
       DepFr_last_answer(dep_fr) = ans_node;
       UNLOCK(DepFr_lock(dep_fr));
       consume_answer_and_procceed(dep_fr, ans_node);
@@ -1172,20 +1174,22 @@
 	if (TrNode_child(ans_node)) {
           /* dependency frame with unconsumed answers */
 #ifdef MODE_DIRECTED_TABLING
-	  ans_node_ptr first_ans_node, aux_ans_node;
-	  first_ans_node = ans_node;
-	  do {
+	  if (IS_INVALID_LEAF_NODE(TrNode_child(ans_node))) {
+	    ans_node_ptr first_ans_node, aux_ans_node;
+	    first_ans_node = ans_node;
 	    ans_node = TrNode_child(ans_node);
-	  } while (IS_INVALID_LEAF_NODE(ans_node));
-	  aux_ans_node = TrNode_child(first_ans_node);
-	  while (aux_ans_node != ans_node) {
-	    TrNode_child(first_ans_node) = ans_node;
-	    first_ans_node = aux_ans_node;
+	    do {
+	      ans_node = TrNode_child(ans_node);
+	    } while (IS_INVALID_LEAF_NODE(ans_node));
 	    aux_ans_node = TrNode_child(first_ans_node);
-	  }
-#else
-          ans_node = TrNode_child(ans_node);
+	    do {
+	      TrNode_child(first_ans_node) = ans_node;
+	      first_ans_node = aux_ans_node;
+	      aux_ans_node = TrNode_child(first_ans_node);
+	    } while (aux_ans_node != ans_node);
+	  } else
 #endif /* MODE_DIRECTED_TABLING */
+	    ans_node = TrNode_child(ans_node);
           DepFr_last_answer(dep_fr) = ans_node;
 #ifdef YAPOR
           if (YOUNGER_CP(DepFr_backchain_cp(dep_fr), top_chain_cp))
@@ -1429,20 +1433,22 @@
       if (TrNode_child(ans_node)) {
         /* dependency frame with unconsumed answers */
 #ifdef MODE_DIRECTED_TABLING
-	ans_node_ptr first_ans_node, aux_ans_node;
-	first_ans_node = ans_node;
-	do {
+	if (IS_INVALID_LEAF_NODE(TrNode_child(ans_node))) {
+	  ans_node_ptr first_ans_node, aux_ans_node;
+	  first_ans_node = ans_node;
 	  ans_node = TrNode_child(ans_node);
-	} while (IS_INVALID_LEAF_NODE(ans_node));
-	aux_ans_node = TrNode_child(first_ans_node);
-	while (aux_ans_node != ans_node) {
-	  TrNode_child(first_ans_node) = ans_node;
-	  first_ans_node = aux_ans_node;
+	  do {
+	    ans_node = TrNode_child(ans_node);
+	  } while (IS_INVALID_LEAF_NODE(ans_node));
 	  aux_ans_node = TrNode_child(first_ans_node);
-	}
-#else
-        ans_node = TrNode_child(ans_node);
+	  do {
+	    TrNode_child(first_ans_node) = ans_node;
+	    first_ans_node = aux_ans_node;
+	    aux_ans_node = TrNode_child(first_ans_node);
+	  } while (aux_ans_node != ans_node);
+	} else
 #endif /* MODE_DIRECTED_TABLING */
+	  ans_node = TrNode_child(ans_node);
         DepFr_last_answer(dep_fr) = ans_node;
         if (B->cp_ap) {
 #ifdef YAPOR
@@ -1602,20 +1608,22 @@
           /* unconsumed answers */
           UNLOCK_OR_FRAME(LOCAL_top_or_fr);
 #ifdef MODE_DIRECTED_TABLING
-	  ans_node_ptr first_ans_node, aux_ans_node;
-	  first_ans_node = ans_node;
-	  do {
+	  if (IS_INVALID_LEAF_NODE(TrNode_child(ans_node))) {
+	    ans_node_ptr first_ans_node, aux_ans_node;
+	    first_ans_node = ans_node;
 	    ans_node = TrNode_child(ans_node);
-	  } while (IS_INVALID_LEAF_NODE(ans_node));
-	  aux_ans_node = TrNode_child(first_ans_node);
-	  while (aux_ans_node != ans_node) {
-	    TrNode_child(first_ans_node) = ans_node;
-	    first_ans_node = aux_ans_node;
+	    do {
+	      ans_node = TrNode_child(ans_node);
+	    } while (IS_INVALID_LEAF_NODE(ans_node));
 	    aux_ans_node = TrNode_child(first_ans_node);
-	  }
-#else
-          ans_node = TrNode_child(ans_node);
+	    do {
+	      TrNode_child(first_ans_node) = ans_node;
+	      first_ans_node = aux_ans_node;
+	      aux_ans_node = TrNode_child(first_ans_node);
+	    } while (aux_ans_node != ans_node);
+	  } else
 #endif /* MODE_DIRECTED_TABLING */
+	    ans_node = TrNode_child(ans_node);
           DepFr_last_answer(LOCAL_top_dep_fr) = ans_node;
           UNLOCK(DepFr_lock(LOCAL_top_dep_fr));
           consume_answer_and_procceed(LOCAL_top_dep_fr, ans_node);
diff --git a/OPTYap/tab.structs.h b/OPTYap/tab.structs.h
index a681d32c1..28dff3422 100644
--- a/OPTYap/tab.structs.h
+++ b/OPTYap/tab.structs.h
@@ -220,13 +220,13 @@ typedef struct subgoal_frame {
   struct answer_trie_node *answer_trie;
   struct answer_trie_node *first_answer;
   struct answer_trie_node *last_answer;
+#ifdef MODE_DIRECTED_TABLING
+  int* mode_directed_array;
+  struct answer_trie_node *invalid_chain;
+#endif /*MODE_DIRECTED_TABLING*/
 #ifdef INCOMPLETE_TABLING
   struct answer_trie_node *try_answer;
 #endif /* INCOMPLETE_TABLING */
-#ifdef MODE_DIRECTED_TABLING
-  struct answer_trie_node *invalid_chain;
-  int* mode_directed_array;
-#endif /*MODE_DIRECTED_TABLING*/
 #ifdef LIMIT_TABLING
   struct subgoal_frame *previous;
 #endif /* LIMIT_TABLING */
@@ -245,9 +245,9 @@ typedef struct subgoal_frame {
 #define SgFr_answer_trie(X)    ((X)->answer_trie)
 #define SgFr_first_answer(X)   ((X)->first_answer)
 #define SgFr_last_answer(X)    ((X)->last_answer)
-#define SgFr_try_answer(X)     ((X)->try_answer)
-#define SgFr_invalid_chain(X)  ((X)->invalid_chain)
 #define SgFr_mode_directed(X)  ((X)->mode_directed_array)
+#define SgFr_invalid_chain(X)  ((X)->invalid_chain)
+#define SgFr_try_answer(X)     ((X)->try_answer)
 #define SgFr_previous(X)       ((X)->previous)
 #define SgFr_next(X)           ((X)->next)
 
@@ -269,11 +269,11 @@ typedef struct subgoal_frame {
                       It is used to check for/insert new answers.
   SgFr_first_answer:  a pointer to the bottom answer trie node of the first available answer.
   SgFr_last_answer:   a pointer to the bottom answer trie node of the last available answer.
+  SgFr_mode_directed: a pointer to the mode directed array.
+  SgFr_invalid_chain: a pointer to the first invalid leaf node when using mode directed tabling.
   SgFr_try_answer:    a pointer to the bottom answer trie node of the last tried answer.
                       It is used when a subgoal was not completed during the previous evaluation.
                       Not completed subgoals start by trying the answers already found.
-  SgFr_invalid_chain: a pointer to the first invalid leaf node when using mode directed tabling.
-  SgFr_mode_directed: a pointer to the mode directed array.
   SgFr_previous:      a pointer to the previous subgoal frame on the chain.
   SgFr_next:          a pointer to the next subgoal frame on the chain.
 
diff --git a/OPTYap/tab.tries.i b/OPTYap/tab.tries.i
index 4278bfe53..c2f0cf0c1 100644
--- a/OPTYap/tab.tries.i
+++ b/OPTYap/tab.tries.i
@@ -56,7 +56,7 @@
 #define LOCK_NODE(NODE)    LOCK_TABLE(NODE)
 #define UNLOCK_NODE(NODE)  UNLOCK_TABLE(NODE)
 #elif defined(TABLE_LOCK_AT_NODE_LEVEL)
-#define LOCK_NODE(NODE)    TRIE_LOCK(TrNode_lock(NODE))
+#define LOCK_NODE(NODE)    LOCK(TrNode_lock(NODE))
 #define UNLOCK_NODE(NODE)  UNLOCK(TrNode_lock(NODE))
 #else /* TABLE_LOCK_AT_ENTRY_LEVEL || ! YAPOR */
 #define LOCK_NODE(NODE)
@@ -1308,7 +1308,9 @@ static void invalidate_answer_trie(ans_node_ptr current_node, sg_fr_ptr sg_fr, i
 	  invalidate_answer_trie(TrNode_child(current_node), sg_fr, TRAVERSE_POSITION_FIRST);
 	  FREE_ANSWER_TRIE_NODE(current_node);
 	} else {
+	  LOCK_NODE(current_ans_node);
 	  TAG_AS_INVALID_LEAF_NODE(current_node);
+	  UNLOCK_NODE(current_ans_node);
 	  TrNode_next(current_node) = SgFr_invalid_chain(sg_fr);
 	  SgFr_invalid_chain(sg_fr) = current_node;
 	}