diff --git a/src/backend/executor/execAmi.c b/src/backend/executor/execAmi.c
index 154301a67f..1381a4a4f0 100644
--- a/src/backend/executor/execAmi.c
+++ b/src/backend/executor/execAmi.c
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.96 2008/07/26 19:15:35 tgl Exp $
+ *	$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.97 2008/08/05 21:28:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -414,9 +414,6 @@ ExecSupportsBackwardScan(Plan *node)
 		case T_Sort:
 			return true;
 
-		case T_Unique:
-			return ExecSupportsBackwardScan(outerPlan(node));
-
 		case T_Limit:
 			return ExecSupportsBackwardScan(outerPlan(node));
 
diff --git a/src/backend/executor/nodeUnique.c b/src/backend/executor/nodeUnique.c
index 545ba848d6..90eb7eeef0 100644
--- a/src/backend/executor/nodeUnique.c
+++ b/src/backend/executor/nodeUnique.c
@@ -3,19 +3,27 @@
  * nodeUnique.c
  *	  Routines to handle unique'ing of queries where appropriate
  *
+ * Unique is a very simple node type that just filters out duplicate
+ * tuples from a stream of sorted tuples from its subplan.  It's essentially
+ * a dumbed-down form of Group: the duplicate-removal functionality is
+ * identical.  However, Unique doesn't do projection nor qual checking,
+ * so it's marginally more efficient for cases where neither is needed.
+ * (It's debatable whether the savings justifies carrying two plan node
+ * types, though.)
+ *
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeUnique.c,v 1.56 2008/01/01 19:45:49 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeUnique.c,v 1.57 2008/08/05 21:28:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 /*
  * INTERFACE ROUTINES
  *		ExecUnique		- generate a unique'd temporary relation
- *		ExecInitUnique	- initialize node and subnodes..
+ *		ExecInitUnique	- initialize node and subnodes
  *		ExecEndUnique	- shutdown node and subnodes
  *
  * NOTES
@@ -32,9 +40,6 @@
 
 /* ----------------------------------------------------------------
  *		ExecUnique
- *
- *		This is a very simple node which filters out duplicate
- *		tuples from a stream of sorted tuples from a subplan.
  * ----------------------------------------------------------------
  */
 TupleTableSlot *				/* return: a tuple or NULL */
@@ -54,11 +59,7 @@ ExecUnique(UniqueState *node)
 	/*
 	 * now loop, returning only non-duplicate tuples. We assume that the
 	 * tuples arrive in sorted order so we can detect duplicates easily.
-	 *
-	 * We return the first tuple from each group of duplicates (or the last
-	 * tuple of each group, when moving backwards).  At either end of the
-	 * subplan, clear the result slot so that we correctly return the
-	 * first/last tuple when reversing direction.
+	 * The first tuple of each group is returned.
 	 */
 	for (;;)
 	{
@@ -68,13 +69,13 @@ ExecUnique(UniqueState *node)
 		slot = ExecProcNode(outerPlan);
 		if (TupIsNull(slot))
 		{
-			/* end of subplan; reset in case we change direction */
+			/* end of subplan, so we're done */
 			ExecClearTuple(resultTupleSlot);
 			return NULL;
 		}
 
 		/*
-		 * Always return the first/last tuple from the subplan.
+		 * Always return the first tuple from the subplan.
 		 */
 		if (TupIsNull(resultTupleSlot))
 			break;
@@ -113,7 +114,7 @@ ExecInitUnique(Unique *node, EState *estate, int eflags)
 	UniqueState *uniquestate;
 
 	/* check for unsupported flags */
-	Assert(!(eflags & EXEC_FLAG_MARK));
+	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
 	/*
 	 * create state structure