diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 66707944a0..2eb862e208 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -848,6 +848,13 @@ inheritance_planner(PlannerInfo *root)
 		 */
 		subroot.rowMarks = (List *) copyObject(root->rowMarks);
 
+		/*
+		 * The append_rel_list likewise might contain references to subquery
+		 * RTEs (if any subqueries were flattenable UNION ALLs).  So prepare
+		 * to apply ChangeVarNodes to that, too.
+		 */
+		subroot.append_rel_list = (List *) copyObject(root->append_rel_list);
+
 		/*
 		 * Add placeholders to the child Query's rangetable list to fill the
 		 * RT indexes already reserved for subqueries in previous children.
@@ -888,6 +895,7 @@ inheritance_planner(PlannerInfo *root)
 					newrti = list_length(subroot.parse->rtable) + 1;
 					ChangeVarNodes((Node *) subroot.parse, rti, newrti, 0);
 					ChangeVarNodes((Node *) subroot.rowMarks, rti, newrti, 0);
+					ChangeVarNodes((Node *) subroot.append_rel_list, rti, newrti, 0);
 					rte = copyObject(rte);
 					subroot.parse->rtable = lappend(subroot.parse->rtable,
 													rte);
@@ -896,7 +904,6 @@ inheritance_planner(PlannerInfo *root)
 			}
 		}
 
-		/* We needn't modify the child's append_rel_list */
 		/* There shouldn't be any OJ or LATERAL info to translate, as yet */
 		Assert(subroot.join_info_list == NIL);
 		Assert(subroot.lateral_info_list == NIL);
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 5c9f3d64ce..333efc2712 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -280,7 +280,8 @@ add_rtes_to_flat_rtable(PlannerInfo *root, bool recursing)
 		 * RTEs without matching RelOptInfos, as they likewise have been
 		 * pulled up.
 		 */
-		if (rte->rtekind == RTE_SUBQUERY && !rte->inh)
+		if (rte->rtekind == RTE_SUBQUERY && !rte->inh &&
+			rti < root->simple_rel_array_size)
 		{
 			RelOptInfo *rel = root->simple_rel_array[rti];
 
diff --git a/src/test/regress/expected/inherit.out b/src/test/regress/expected/inherit.out
index bfe67337b7..c84c435a8a 100644
--- a/src/test/regress/expected/inherit.out
+++ b/src/test/regress/expected/inherit.out
@@ -557,8 +557,7 @@ insert into bar2 values(2,2,2);
 insert into bar2 values(3,3,3);
 insert into bar2 values(4,4,4);
 update bar set f2 = f2 + 100 where f1 in (select f1 from foo);
-SELECT relname, bar.* FROM bar, pg_class where bar.tableoid = pg_class.oid
-order by 1,2;
+select tableoid::regclass::text as relname, bar.* from bar order by 1,2;
  relname | f1 | f2  
 ---------+----+-----
  bar     |  1 | 101
@@ -571,6 +570,24 @@ order by 1,2;
  bar2    |  4 |   4
 (8 rows)
 
+-- Check UPDATE with inherited target and an appendrel subquery
+update bar set f2 = f2 + 100
+from
+  ( select f1 from foo union all select f1+3 from foo ) ss
+where bar.f1 = ss.f1;
+select tableoid::regclass::text as relname, bar.* from bar order by 1,2;
+ relname | f1 | f2  
+---------+----+-----
+ bar     |  1 | 201
+ bar     |  2 | 202
+ bar     |  3 | 203
+ bar     |  4 | 104
+ bar2    |  1 | 201
+ bar2    |  2 | 202
+ bar2    |  3 | 203
+ bar2    |  4 | 104
+(8 rows)
+
 /* Test multiple inheritance of column defaults */
 CREATE TABLE firstparent (tomorrow date default now()::date + 1);
 CREATE TABLE secondparent (tomorrow date default  now() :: date  +  1);
diff --git a/src/test/regress/sql/inherit.sql b/src/test/regress/sql/inherit.sql
index 747aa88666..09bb7507ad 100644
--- a/src/test/regress/sql/inherit.sql
+++ b/src/test/regress/sql/inherit.sql
@@ -118,8 +118,15 @@ insert into bar2 values(4,4,4);
 
 update bar set f2 = f2 + 100 where f1 in (select f1 from foo);
 
-SELECT relname, bar.* FROM bar, pg_class where bar.tableoid = pg_class.oid
-order by 1,2;
+select tableoid::regclass::text as relname, bar.* from bar order by 1,2;
+
+-- Check UPDATE with inherited target and an appendrel subquery
+update bar set f2 = f2 + 100
+from
+  ( select f1 from foo union all select f1+3 from foo ) ss
+where bar.f1 = ss.f1;
+
+select tableoid::regclass::text as relname, bar.* from bar order by 1,2;
 
 /* Test multiple inheritance of column defaults */