diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index e90e1d6..31d4331 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -1779,8 +1779,19 @@ flatten_grouping_sets(Node *expr, bool toplevel, bool *hasGroupingSets)
 				RowExpr    *r = (RowExpr *) expr;
 
 				if (r->row_format == COERCE_IMPLICIT_CAST)
-					return flatten_grouping_sets((Node *) r->args,
-												 false, NULL);
+				{
+					Node   *n1 = flatten_grouping_sets((Node *) r->args,
+													   false, NULL);
+
+					/*
+					 * Make a list for row expression if toplevel is false,
+					 * return flatten list otherwise
+					 */
+					if (toplevel)
+						return (Node *) n1;
+					else
+						return (Node *) list_make1(n1);
+				}
 			}
 			break;
 		case T_GroupingSet:
@@ -1805,7 +1816,10 @@ flatten_grouping_sets(Node *expr, bool toplevel, bool *hasGroupingSets)
 				{
 					Node	   *n2 = flatten_grouping_sets(lfirst(l2), false, NULL);
 
-					result_set = lappend(result_set, n2);
+					if (IsA(n2, List))
+						result_set = list_concat(result_set, (List *) n2);
+					else
+						result_set = lappend(result_set, n2);
 				}
 
 				/*
diff --git a/src/test/regress/expected/groupingsets.out b/src/test/regress/expected/groupingsets.out
index adb39b3..5c47717 100644
--- a/src/test/regress/expected/groupingsets.out
+++ b/src/test/regress/expected/groupingsets.out
@@ -145,6 +145,112 @@ select a, b, sum(c), sum(sum(c)) over (order by a,b) as rsum
    |   |  12 |   36
 (6 rows)
 
+-- nesting with grouping sets
+select sum(c) from gstest2
+  group by grouping sets((), grouping sets((), grouping sets(())))
+  order by 1 desc;
+ sum 
+-----
+  12
+  12
+  12
+(3 rows)
+
+select sum(c) from gstest2
+  group by grouping sets((), grouping sets((), grouping sets(((a, b)))))
+  order by 1 desc;
+ sum 
+-----
+  12
+  12
+   8
+   2
+   2
+(5 rows)
+
+select sum(c) from gstest2
+  group by grouping sets(grouping sets(rollup(c), grouping sets(cube(c))))
+  order by 1 desc;
+ sum 
+-----
+  12
+  12
+   6
+   6
+   6
+   6
+(6 rows)
+
+select sum(c) from gstest2
+  group by grouping sets(a, grouping sets(a, cube(b)))
+  order by 1 desc;
+ sum 
+-----
+  12
+  10
+  10
+   8
+   4
+   2
+   2
+(7 rows)
+
+select sum(c) from gstest2
+  group by grouping sets(grouping sets((a, (b))))
+  order by 1 desc;
+ sum 
+-----
+   8
+   2
+   2
+(3 rows)
+
+select sum(c) from gstest2
+  group by grouping sets(grouping sets((a, b)))
+  order by 1 desc;
+ sum 
+-----
+   8
+   2
+   2
+(3 rows)
+
+select sum(c) from gstest2
+  group by grouping sets(grouping sets(a, grouping sets(a), a))
+  order by 1 desc;
+ sum 
+-----
+  10
+  10
+  10
+   2
+   2
+   2
+(6 rows)
+
+select sum(c) from gstest2
+  group by grouping sets(grouping sets(a, grouping sets(a, grouping sets(a), ((a)), a, grouping sets(a), (a)), a))
+  order by 1 desc;
+ sum 
+-----
+  10
+  10
+  10
+  10
+  10
+  10
+  10
+  10
+   2
+   2
+   2
+   2
+   2
+   2
+   2
+   2
+(16 rows)
+
 -- empty input: first is 0 rows, second 1, third 3 etc.
 select a, b, sum(v), count(*) from gstest_empty group by grouping sets ((a,b),a);
  a | b | sum | count 
diff --git a/src/test/regress/sql/groupingsets.sql b/src/test/regress/sql/groupingsets.sql
index 0883afd..e478d34 100644
--- a/src/test/regress/sql/groupingsets.sql
+++ b/src/test/regress/sql/groupingsets.sql
@@ -73,6 +73,32 @@ select grouping(a), a, array_agg(b),
 select a, b, sum(c), sum(sum(c)) over (order by a,b) as rsum
   from gstest2 group by rollup (a,b) order by rsum, a, b;
 
+-- nesting with grouping sets
+select sum(c) from gstest2
+  group by grouping sets((), grouping sets((), grouping sets(())))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets((), grouping sets((), grouping sets(((a, b)))))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets(grouping sets(rollup(c), grouping sets(cube(c))))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets(a, grouping sets(a, cube(b)))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets(grouping sets((a, (b))))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets(grouping sets((a, b)))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets(grouping sets(a, grouping sets(a), a))
+  order by 1 desc;
+select sum(c) from gstest2
+  group by grouping sets(grouping sets(a, grouping sets(a, grouping sets(a), ((a)), a, grouping sets(a), (a)), a))
+  order by 1 desc;
+
 -- empty input: first is 0 rows, second 1, third 3 etc.
 select a, b, sum(v), count(*) from gstest_empty group by grouping sets ((a,b),a);
 select a, b, sum(v), count(*) from gstest_empty group by grouping sets ((a,b),());