diff --git a/executor/executor_test.go b/executor/executor_test.go
index bb97f1770acab..67168cf725b66 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -5378,3 +5378,15 @@ func (s *testSuite1) TestIssue15718(c *C) {
 	tk.MustExec("insert into tt values(0, '2', null), (7, null, '1122'), (NULL, 'w', null), (NULL, '2', '3344'), (NULL, NULL, '0'), (7, 'f', '33');")
 	tk.MustQuery("select a and b as d, a or c as e from tt;").Check(testkit.Rows("0 <nil>", "<nil> 1", "0 <nil>", "<nil> 1", "<nil> <nil>", "0 1"))
 }
+
+func (s *testSuite1) TestIssue15767(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test;")
+	tk.MustExec("drop table if exists tt;")
+	tk.MustExec("create table t(a int, b char);")
+	tk.MustExec("insert into t values (1,'s'),(2,'b'),(1,'c'),(2,'e'),(1,'a');")
+	tk.MustExec("insert into t select * from t;")
+	tk.MustExec("insert into t select * from t;")
+	tk.MustExec("insert into t select * from t;")
+	tk.MustQuery("select b, count(*) from ( select b from t order by a limit 20 offset 2) as s group by b order by b;").Check(testkit.Rows("a 6", "c 7", "s 7"))
+}
diff --git a/store/mockstore/mocktikv/executor.go b/store/mockstore/mocktikv/executor.go
index 5668707c644d9..c812d435fbaa6 100644
--- a/store/mockstore/mocktikv/executor.go
+++ b/store/mockstore/mocktikv/executor.go
@@ -567,6 +567,7 @@ func (e *topNExec) Next(ctx context.Context) (value [][]byte, err error) {
 				return nil, errors.Trace(err)
 			}
 			if !hasMore {
+				sort.Sort(&e.heap.topNSorter)
 				break
 			}
 		}
@@ -575,7 +576,6 @@ func (e *topNExec) Next(ctx context.Context) (value [][]byte, err error) {
 	if e.cursor >= len(e.heap.rows) {
 		return nil, nil
 	}
-	sort.Sort(&e.heap.topNSorter)
 	row := e.heap.rows[e.cursor]
 	e.cursor++