diff --git a/src/test/regress/expected/groupingsets.out b/src/test/regress/expected/groupingsets.out
index 1374710087b..fd618afe603 100644
--- a/src/test/regress/expected/groupingsets.out
+++ b/src/test/regress/expected/groupingsets.out
@@ -1383,6 +1383,7 @@ select array(select row(v.a,s1.*) from (select two,four, count(*) from onek grou
 (2 rows)
 
 -- test the knapsack
+set enable_indexscan = false;
 set work_mem = '64kB';
 explain (costs off)
   select unique1,
diff --git a/src/test/regress/sql/groupingsets.sql b/src/test/regress/sql/groupingsets.sql
index 0e023d9ddc5..564ebc9b051 100644
--- a/src/test/regress/sql/groupingsets.sql
+++ b/src/test/regress/sql/groupingsets.sql
@@ -355,6 +355,7 @@ select array(select row(v.a,s1.*) from (select two,four, count(*) from onek grou
 
 -- test the knapsack
 
+set enable_indexscan = false;
 set work_mem = '64kB';
 explain (costs off)
   select unique1,