diff --git a/mysql-test/main/subselect.result b/mysql-test/main/subselect.result
index 3ceba6d6feb5f..82dd5f77d8728 100644
--- a/mysql-test/main/subselect.result
+++ b/mysql-test/main/subselect.result
@@ -7642,3 +7642,13 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
diff --git a/mysql-test/main/subselect.test b/mysql-test/main/subselect.test
index 371cf80986311..370b9489309e8 100644
--- a/mysql-test/main/subselect.test
+++ b/mysql-test/main/subselect.test
@@ -6501,3 +6501,13 @@ DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 
 --echo # End of 10.10 tests
+
+--echo #
+--echo # MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+--echo #
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+drop table t1;
+
+--echo # End of 12.2 tests
diff --git a/mysql-test/main/subselect_no_exists_to_in.result b/mysql-test/main/subselect_no_exists_to_in.result
index 7d80763c25a38..bb6260f741576 100644
--- a/mysql-test/main/subselect_no_exists_to_in.result
+++ b/mysql-test/main/subselect_no_exists_to_in.result
@@ -7644,6 +7644,16 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set optimizer_switch=default;
 select @@optimizer_switch like '%exists_to_in=off%';
 @@optimizer_switch like '%exists_to_in=off%'
diff --git a/mysql-test/main/subselect_no_mat.result b/mysql-test/main/subselect_no_mat.result
index 0220a028fcbf4..168a1c64d7389 100644
--- a/mysql-test/main/subselect_no_mat.result
+++ b/mysql-test/main/subselect_no_mat.result
@@ -7639,6 +7639,16 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set optimizer_switch=default;
 select @@optimizer_switch like '%materialization=on%';
 @@optimizer_switch like '%materialization=on%'
diff --git a/mysql-test/main/subselect_no_opts.result b/mysql-test/main/subselect_no_opts.result
index 78eecf8d88f4e..4e3719d2593ca 100644
--- a/mysql-test/main/subselect_no_opts.result
+++ b/mysql-test/main/subselect_no_opts.result
@@ -7637,4 +7637,14 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set @optimizer_switch_for_subselect_test=null;
diff --git a/mysql-test/main/subselect_no_scache.result b/mysql-test/main/subselect_no_scache.result
index 91eecfdb0711b..74684b673ef08 100644
--- a/mysql-test/main/subselect_no_scache.result
+++ b/mysql-test/main/subselect_no_scache.result
@@ -7648,6 +7648,16 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set optimizer_switch=default;
 select @@optimizer_switch like '%subquery_cache=on%';
 @@optimizer_switch like '%subquery_cache=on%'
diff --git a/mysql-test/main/subselect_no_semijoin.result b/mysql-test/main/subselect_no_semijoin.result
index fb0fc0a687451..1a9523a5b9f9e 100644
--- a/mysql-test/main/subselect_no_semijoin.result
+++ b/mysql-test/main/subselect_no_semijoin.result
@@ -7638,6 +7638,16 @@ DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
 #
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
+#
 # MDEV-19714: JOIN::pseudo_bits_cond is not visible in EXPLAIN FORMAT=JSON
 #
 CREATE TABLE t1 ( a INT );
diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 9b60977f2735d..c358cd913c0dc 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -5160,13 +5160,20 @@ bool st_select_lex::optimize_unflattened_subqueries(bool const_only)
       bool has_rand= false;
       for (SELECT_LEX *sl= un->first_select(); sl && !has_rand;
            sl= sl->next_select())
-        has_rand= sl->uncacheable & UNCACHEABLE_RAND;
+        has_rand= (sl->uncacheable & UNCACHEABLE_RAND);
       if (has_rand)
       {
         for (SELECT_LEX *sl= un->first_select(); sl; sl= sl->next_select())
           sl->uncacheable |= UNCACHEABLE_UNITED;
       }
 
+      /*
+        If any SELECT in the unit is marked as UNCACHEABLE_RAND, then the
+        unit itself should also be marked as UNCACHEABLE_RAND.
+      */
+      DBUG_ASSERT(has_rand ==
+                  static_cast<bool>(un->uncacheable & UNCACHEABLE_RAND));
+
       if (is_correlated_unit)
       {
         /*
@@ -11403,6 +11410,7 @@ SELECT_LEX_UNIT *LEX::parsed_select_expr_cont(SELECT_LEX_UNIT *unit,
   }
   last->link_neighbour(sel1);
   sel1->set_master_unit(unit);
+  unit->uncacheable|= sel1->uncacheable;
   sel1->set_linkage_and_distinct(unit_type, distinct);
   unit->pre_last_parse= last;
   return unit;