diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index ce8a2e66fe4..d14d80973e4 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -776,6 +776,9 @@ pull_var_clause_walker(Node *node, pull_var_clause_context *context)
  * PlaceHolderVar or constructed from those, we can just add the
  * varnullingrels bits to the existing nullingrels field(s); otherwise
  * we have to add a PlaceHolderVar wrapper.
+ *
+ * If root is NULL, nulled whole-row JOIN Vars are left unexpanded, so the
+ * result must be flattened again with a root before it can be executed.
  */
 Node *
 flatten_join_alias_vars(PlannerInfo *root, Query *query, Node *node)
@@ -809,7 +812,8 @@ flatten_join_alias_vars(PlannerInfo *root, Query *query, Node *node)
  * PlaceHolderVars.  We can avoid making PlaceHolderVars in the parser's
  * usage because it won't be dealing with arbitrary expressions: so long as
  * adjust_standard_join_alias_expression can handle everything the parser
- * would make as a join alias expression, we're OK.
+ * would make as a join alias expression, we're OK.  (Nulled whole-row join
+ * Vars are the exception; those are left unexpanded.)
  *
  * The "node" might be part of a sub-query of the Query whose join alias
  * Vars are to be expanded.  "sublevels_up" indicates how far below the
@@ -865,6 +869,13 @@ flatten_join_alias_vars_mutator(Node *node,
 			ListCell   *lv;
 			ListCell   *ln;
 
+			/*
+			 * A nulled whole-row expansion needs a PlaceHolderVar, which we
+			 * can't make without a root; leave the Var unexpanded.
+			 */
+			if (context->root == NULL && var->varnullingrels != NULL)
+				return node;
+
 			Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
 			forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
 			{
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 25a9a39cdc1..b0cab6a7823 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -4422,6 +4422,35 @@ group by t1.q2 order by 1;
   4567890123456789 |     6
 (4 rows)
 
+-- nulled whole-row Var of a join alias in aggregate queries
+select t1.q2, count(t23)
+from int8_tbl t1 left join
+  (int8_tbl t2 join int4_tbl t3 on t3.f1 = 0) t23
+  on (t1.q2 = t23.q1)
+group by t1.q2 order by 1;
+        q2         | count 
+-------------------+-------
+ -4567890123456789 |     0
+               123 |     2
+               456 |     0
+  4567890123456789 |     6
+(4 rows)
+
+select t23, count(*)
+from int8_tbl t1 left join
+  (int8_tbl t2 join int4_tbl t3 on t3.f1 = 0) t23
+  on (t1.q2 = t23.q1)
+group by t23 order by 1;
+                  t23                   | count 
+----------------------------------------+-------
+ (123,456,0)                            |     1
+ (123,4567890123456789,0)               |     1
+ (4567890123456789,-4567890123456789,0) |     2
+ (4567890123456789,123,0)               |     2
+ (4567890123456789,4567890123456789,0)  |     2
+                                        |     2
+(6 rows)
+
 --
 -- test incorrect failure to NULL pulled-up subexpressions
 --
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 7a431b926ea..4fc0ded779d 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -1384,6 +1384,19 @@ from int8_tbl t1 left join
   on (t1.q2 = t2.q1)
 group by t1.q2 order by 1;
 
+-- nulled whole-row Var of a join alias in aggregate queries
+select t1.q2, count(t23)
+from int8_tbl t1 left join
+  (int8_tbl t2 join int4_tbl t3 on t3.f1 = 0) t23
+  on (t1.q2 = t23.q1)
+group by t1.q2 order by 1;
+
+select t23, count(*)
+from int8_tbl t1 left join
+  (int8_tbl t2 join int4_tbl t3 on t3.f1 = 0) t23
+  on (t1.q2 = t23.q1)
+group by t23 order by 1;
+
 --
 -- test incorrect failure to NULL pulled-up subexpressions
 --