diff --git a/planner/core/integration_test.go b/planner/core/integration_test.go
index 521e928a12edf..cdcc4bfbac1e9 100644
--- a/planner/core/integration_test.go
+++ b/planner/core/integration_test.go
@@ -8797,3 +8797,11 @@ WHERE res.state != 2
 ORDER BY res.branch_id;
 `, errno.ErrNotSupportedYet)
 }
+
+func TestIssue40285(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("CREATE TABLE t(col1 enum('p5', '9a33x') NOT NULL DEFAULT 'p5',col2 tinyblob DEFAULT NULL) ENGINE = InnoDB DEFAULT CHARSET = latin1 COLLATE = latin1_bin;")
+	tk.MustQuery("(select last_value(col1) over () as r0 from t) union all (select col2 as r0 from t);")
+}
diff --git a/planner/core/logical_plan_builder.go b/planner/core/logical_plan_builder.go
index 02cd8e00d7b36..3c330c341d728 100644
--- a/planner/core/logical_plan_builder.go
+++ b/planner/core/logical_plan_builder.go
@@ -1729,7 +1729,9 @@ func (*PlanBuilder) setUnionFlen(resultTp *types.FieldType, cols []expression.Ex
 		childTp := cols[i].GetType()
 		childTpCharLen := 1
 		if isBinary {
-			childTpCharLen = charset.CharacterSetInfos[childTp.GetCharset()].Maxlen
+			if charsetInfo, ok := charset.CharacterSetInfos[childTp.GetCharset()]; ok {
+				childTpCharLen = charsetInfo.Maxlen
+			}
 		}
 		resultTp.SetFlen(mathutil.Max(resultTp.GetFlen(), childTpCharLen*childTp.GetFlen()))
 	}
diff --git a/planner/core/plan_cost_ver2_test.go b/planner/core/plan_cost_ver2_test.go
index f6384a14f3cf7..16540cb784fa2 100644
--- a/planner/core/plan_cost_ver2_test.go
+++ b/planner/core/plan_cost_ver2_test.go
@@ -177,6 +177,7 @@ func TestCostModelVer2ScanRowSize(t *testing.T) {
 	tk.MustExec(`create table t (pk int, a int, b int, c int, d int, primary key(pk), index ab(a, b), index abc(a, b, c))`)
 	tk.MustExec("insert into t values (1, 1, 1, 1, 1)")
 	tk.MustExec(`set @@tidb_cost_model_version=2`)
+	tk.MustExec("set global tidb_enable_collect_execution_info=1;")
 
 	cases := []struct {
 		query       string