diff --git a/src/backend/gpopt/translate/CTranslatorUtils.cpp b/src/backend/gpopt/translate/CTranslatorUtils.cpp
index 0887c72725c..90e0a70ba23 100644
--- a/src/backend/gpopt/translate/CTranslatorUtils.cpp
+++ b/src/backend/gpopt/translate/CTranslatorUtils.cpp
@@ -918,7 +918,7 @@ CTranslatorUtils::GetColumnAttnosForGroupBy(
 			case GROUPING_SET_EMPTY:
 			{
 				col_attnos_arr_current = GPOS_NEW(mp) CBitSetArray(mp);
-				CBitSet *bset = GPOS_NEW(mp) CBitSet(mp);
+				CBitSet *bset = GPOS_NEW(mp) CBitSet(mp, num_cols);
 				col_attnos_arr_current->Append(bset);
 				break;
 			}
@@ -1113,11 +1113,12 @@ CTranslatorUtils::CreateGroupingSetsForRollup(CMemoryPool *mp,
 	GPOS_ASSERT(grouping_set->kind == GROUPING_SET_ROLLUP);
 	CBitSetArray *col_attnos_arr = GPOS_NEW(mp) CBitSetArray(mp);
 	ListCell *lc = nullptr;
-	CBitSet *current_result = GPOS_NEW(mp) CBitSet(mp);
+
+	CBitSet *current_result = GPOS_NEW(mp) CBitSet(mp, num_cols);
 	// Maintaining the order of grouping sets is essential because the
 	// UnionAll operator matches each child's distribution with the
 	// distribution of the first child
-	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp));
+	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp, num_cols));
 	ForEach(lc, grouping_set->content)
 	{
 		GroupingSet *gs_current = (GroupingSet *) lfirst(lc);
@@ -1152,8 +1153,9 @@ CTranslatorUtils::CreateGroupingSetsForCube(CMemoryPool *mp,
 	GPOS_ASSERT(grouping_set->kind == GROUPING_SET_CUBE);
 	CBitSetArray *col_attnos_arr = GPOS_NEW(mp) CBitSetArray(mp);
 
-	// add an empty set
-	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp));
+	// add an empty set — vec_size must match what CreateAttnoSetForGroupingSet
+	// produces (num_cols), otherwise Union below leaves misaligned links.
+	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp, num_cols));
 
 	ListCell *lc = nullptr;
 	ForEach(lc, grouping_set->content)
diff --git a/src/backend/gporca/libgpos/src/common/CBitSet.cpp b/src/backend/gporca/libgpos/src/common/CBitSet.cpp
index 1eb9d2c939f..c3d7703f59d 100644
--- a/src/backend/gporca/libgpos/src/common/CBitSet.cpp
+++ b/src/backend/gporca/libgpos/src/common/CBitSet.cpp
@@ -347,6 +347,8 @@ CBitSet::ExchangeClear(ULONG pos)
 void
 CBitSet::Union(const CBitSet *pbsOther)
 {
+	GPOS_ASSERT(m_vector_size == pbsOther->m_vector_size);
+
 	CBitSetLink *bsl = nullptr;
 	CBitSetLink *bsl_other = nullptr;
 
@@ -425,6 +427,10 @@ CBitSet::Intersection(const CBitSet *pbsOther)
 		return;
 	}
 
+	// See CBitSet::Union: link offsets depend on m_vector_size, so mixing
+	// bitsets with different sizes makes FindLinkByOffset miss links.
+	GPOS_ASSERT(m_vector_size == pbsOther->m_vector_size);
+
 	CBitSetLink *bsl_other = nullptr;
 	CBitSetLink *bsl = m_bsllist.First();
 
diff --git a/src/test/regress/expected/groupingsets.out b/src/test/regress/expected/groupingsets.out
index 5222cc22b70..a1cb32e2478 100644
--- a/src/test/regress/expected/groupingsets.out
+++ b/src/test/regress/expected/groupingsets.out
@@ -2470,4 +2470,32 @@ group by rollup (a,b) order by a;
    |   |    6
 (8 rows)
 
+-- ORCA: rollup over a derived-expression group alias with a target-list SRF.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by rollup(a, ab) order by 1,2;
+ g | ab 
+---+----
+ 1 |  2
+ 1 |  4
+ 1 |   
+ 1 |   
+ 2 |  4
+ 2 |   
+(6 rows)
+
+-- Same shape with cube(): exercises additional grouping-set combinations.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by cube(a, ab) order by 1,2;
+ g | ab 
+---+----
+ 1 |  2
+ 1 |  4
+ 1 |   
+ 1 |   
+ 2 |  4
+ 2 |   
+(6 rows)
+
 -- end
diff --git a/src/test/regress/expected/groupingsets_optimizer.out b/src/test/regress/expected/groupingsets_optimizer.out
index a07017eca32..f02364c362b 100644
--- a/src/test/regress/expected/groupingsets_optimizer.out
+++ b/src/test/regress/expected/groupingsets_optimizer.out
@@ -2645,4 +2645,32 @@ group by rollup (a,b) order by a;
    |   |    6
 (8 rows)
 
+-- ORCA: rollup over a derived-expression group alias with a target-list SRF.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by rollup(a, ab) order by 1,2;
+ g | ab 
+---+----
+ 1 |  2
+ 1 |  4
+ 1 |   
+ 1 |   
+ 2 |  4
+ 2 |   
+(6 rows)
+
+-- Same shape with cube(): exercises additional grouping-set combinations.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by cube(a, ab) order by 1,2;
+ g | ab 
+---+----
+ 1 |  2
+ 1 |  4
+ 1 |   
+ 1 |   
+ 2 |  4
+ 2 |   
+(6 rows)
+
 -- end
diff --git a/src/test/regress/sql/groupingsets.sql b/src/test/regress/sql/groupingsets.sql
index 851a1eea6bb..f7bcba8a46a 100644
--- a/src/test/regress/sql/groupingsets.sql
+++ b/src/test/regress/sql/groupingsets.sql
@@ -723,4 +723,14 @@ select a, b, rank(b) within group (order by b nulls last)
 from (values (1,1),(1,4),(1,5),(3,1),(3,2)) v(a,b)
 group by rollup (a,b) order by a;
 
+-- ORCA: rollup over a derived-expression group alias with a target-list SRF.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by rollup(a, ab) order by 1,2;
+
+-- Same shape with cube(): exercises additional grouping-set combinations.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by cube(a, ab) order by 1,2;
+
 -- end