diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index 0d46e096e5..ca38e78f21 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -2879,6 +2879,37 @@ FROM t1 WHERE c2 < 100 GROUP BY c1 ORDER BY 2;
 (10 rows)
 
 DROP TABLE t1 CASCADE;
+-- Check, that GROUP-BY reordering optimization can operate with pathkeys, built
+-- by planner itself. For example, by MergeJoin.
+SET enable_hashjoin = off;
+SET enable_nestloop = off;
+explain (COSTS OFF)
+SELECT c1.relname,c1.relpages
+FROM pg_class c1 JOIN pg_class c2 ON (c1.relname=c2.relname AND c1.relpages=c2.relpages)
+GROUP BY c1.reltuples,c1.relpages,c1.relname
+ORDER BY c1.relpages, c1.relname, c1.relpages*c1.relpages;
+                                         QUERY PLAN                                          
+---------------------------------------------------------------------------------------------
+ Incremental Sort
+   Sort Key: c1.relpages, c1.relname, ((c1.relpages * c1.relpages))
+   Presorted Key: c1.relpages, c1.relname
+   ->  Group
+         Group Key: c1.relpages, c1.relname, c1.reltuples
+         ->  Incremental Sort
+               Sort Key: c1.relpages, c1.relname, c1.reltuples
+               Presorted Key: c1.relpages, c1.relname
+               ->  Merge Join
+                     Merge Cond: ((c1.relpages = c2.relpages) AND (c1.relname = c2.relname))
+                     ->  Sort
+                           Sort Key: c1.relpages, c1.relname
+                           ->  Seq Scan on pg_class c1
+                     ->  Sort
+                           Sort Key: c2.relpages, c2.relname
+                           ->  Seq Scan on pg_class c2
+(16 rows)
+
+RESET enable_hashjoin;
+RESET enable_nestloop;
 RESET enable_hashagg;
 RESET max_parallel_workers;
 RESET max_parallel_workers_per_gather;
diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index f99167ac9e..cf87b5d5dd 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -1233,6 +1233,18 @@ SELECT array_agg(c1 ORDER BY c2),c2
 FROM t1 WHERE c2 < 100 GROUP BY c1 ORDER BY 2;
 DROP TABLE t1 CASCADE;
 
+-- Check, that GROUP-BY reordering optimization can operate with pathkeys, built
+-- by planner itself. For example, by MergeJoin.
+SET enable_hashjoin = off;
+SET enable_nestloop = off;
+explain (COSTS OFF)
+SELECT c1.relname,c1.relpages
+FROM pg_class c1 JOIN pg_class c2 ON (c1.relname=c2.relname AND c1.relpages=c2.relpages)
+GROUP BY c1.reltuples,c1.relpages,c1.relname
+ORDER BY c1.relpages, c1.relname, c1.relpages*c1.relpages;
+RESET enable_hashjoin;
+RESET enable_nestloop;
+
 RESET enable_hashagg;
 RESET max_parallel_workers;
 RESET max_parallel_workers_per_gather;