diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index b71cf6dae2e..70543613fe2 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.133 2007/08/31 01:44:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.134 2007/10/04 20:44:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -136,6 +136,40 @@ build_base_rel_tlists(PlannerInfo *root, List *final_tlist)
 	}
 }
 
+/*
+ * add_IN_vars_to_tlists
+ *	  Add targetlist entries for each var needed in InClauseInfo entries
+ *	  to the appropriate base relations.
+ *
+ * Normally this is a waste of time because scanning of the WHERE clause
+ * will have added them.  But it is possible that eval_const_expressions()
+ * simplified away all references to the vars after the InClauseInfos were
+ * made.  We need the IN's righthand-side vars to be available at the join
+ * anyway, in case we try to unique-ify the subselect's outputs.  (The only
+ * known case that provokes this is "WHERE false AND foo IN (SELECT ...)".
+ * We don't try to be very smart about such cases, just correct.)
+ */
+void
+add_IN_vars_to_tlists(PlannerInfo *root)
+{
+	ListCell   *l;
+
+	foreach(l, root->in_info_list)
+	{
+		InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
+		List	   *in_vars;
+
+		in_vars = pull_var_clause((Node *) ininfo->sub_targetlist, false);
+		if (in_vars != NIL)
+		{
+			add_vars_to_targetlist(root, in_vars,
+								   bms_union(ininfo->lefthand,
+											 ininfo->righthand));
+			list_free(in_vars);
+		}
+	}
+}
+
 /*
  * add_vars_to_targetlist
  *	  For each variable appearing in the list, add it to the owning
diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index f8ff3a71508..772ee84e8d5 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planmain.c,v 1.102 2007/07/07 20:46:45 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planmain.c,v 1.103 2007/10/04 20:44:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -211,6 +211,13 @@ query_planner(PlannerInfo *root, List *tlist,
 
 	joinlist = deconstruct_jointree(root);
 
+	/*
+	 * Vars mentioned in InClauseInfo items also have to be added to baserel
+	 * targetlists.  Nearly always, they'd have got there from the original
+	 * WHERE qual, but in corner cases maybe not.
+	 */
+	add_IN_vars_to_tlists(root);
+
 	/*
 	 * Reconsider any postponed outer-join quals now that we have built up
 	 * equivalence classes.  (This could result in further additions or
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 319c38c66b5..4673d53098f 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.101 2007/05/04 01:13:45 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/planmain.h,v 1.102 2007/10/04 20:44:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -72,6 +72,7 @@ extern int	join_collapse_limit;
 
 extern void add_base_rels_to_query(PlannerInfo *root, Node *jtnode);
 extern void build_base_rel_tlists(PlannerInfo *root, List *final_tlist);
+extern void add_IN_vars_to_tlists(PlannerInfo *root);
 extern void add_vars_to_targetlist(PlannerInfo *root, List *vars,
 								   Relids where_needed);
 extern List *deconstruct_jointree(PlannerInfo *root);