diff --git a/mysql-test/r/subselect.result b/mysql-test/r/subselect.result
index 41fba93db5b..1db31881607 100644
--- a/mysql-test/r/subselect.result
+++ b/mysql-test/r/subselect.result
@@ -1239,3 +1239,15 @@ insert into t2 values (1);
 update t1 set  s1 = s1 + 1 where 1 = (select x.s1 as A from t2 WHERE t2.s1 > t1.s1 order by A);
 ERROR 42S02: Unknown table 'x' in field list
 DROP TABLE t1, t2;
+create table t1 (a int) type=innodb;
+create table t2 (a int) type=innodb;
+create table t3 (a int) type=innodb;
+insert into t1 values (1),(2),(3),(4);
+insert into t2 values (10),(20),(30),(40);
+insert into t3 values (1),(2),(10),(50);
+select a from t3 where t3.a in (select a from t1 where a <= 3 union select * from t2 where a <= 30);
+a
+1
+2
+10
+drop table t1,t2;
diff --git a/mysql-test/t/subselect.test b/mysql-test/t/subselect.test
index 1d7da94d455..28408bbf365 100644
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@@ -841,3 +841,15 @@ insert into t2 values (1);
 update t1 set  s1 = s1 + 1 where 1 = (select x.s1 as A from t2 WHERE t2.s1 > t1.s1 order by A);
 DROP TABLE t1, t2;
 
+#
+# UNION unlocking test
+#
+create table t1 (a int) type=innodb;
+create table t2 (a int) type=innodb;
+create table t3 (a int) type=innodb;
+insert into t1 values (1),(2),(3),(4);
+insert into t2 values (10),(20),(30),(40);
+insert into t3 values (1),(2),(10),(50);
+select a from t3 where t3.a in (select a from t1 where a <= 3 union select * from t2 where a <= 30);
+drop table t1,t2;
+
diff --git a/sql/sql_union.cc b/sql/sql_union.cc
index 57044a8370a..41fc754e754 100644
--- a/sql/sql_union.cc
+++ b/sql/sql_union.cc
@@ -354,7 +354,8 @@ int st_select_lex_unit::exec()
 			global_parameters->order_list.elements,
 			(ORDER*)global_parameters->order_list.first,
 			(ORDER*) NULL, NULL, (ORDER*) NULL,
-			thd->options, result, this, fake_select, 0);
+			thd->options | SELECT_NO_UNLOCK,
+			result, this, fake_select, 0);
       if (found_rows_for_union && !res)
 	thd->limit_found_rows = (ulonglong)table->file->records;
       fake_select->exclude();