diff --git a/planner/core/integration_test.go b/planner/core/integration_test.go
index 459d113d97f2c..0eb7bea667b9a 100644
--- a/planner/core/integration_test.go
+++ b/planner/core/integration_test.go
@@ -8219,3 +8219,11 @@ func TestAutoIncrementCheckWithCheckConstraint(t *testing.T) {
 		KEY idx_autoinc_id (id)
 	)`)
 }
+
+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 df903670ab010..21c54056c7cd8 100644
--- a/planner/core/logical_plan_builder.go
+++ b/planner/core/logical_plan_builder.go
@@ -1576,7 +1576,9 @@ 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 38ee51738d81a..c56f41b22cf59 100644
--- a/planner/core/plan_cost_ver2_test.go
+++ b/planner/core/plan_cost_ver2_test.go
@@ -163,6 +163,7 @@ 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