diff --git a/mysql-test/main/alter_table_online_debug.result b/mysql-test/main/alter_table_online_debug.result
index 81fe415cf6f..3bb2bce8052 100644
--- a/mysql-test/main/alter_table_online_debug.result
+++ b/mysql-test/main/alter_table_online_debug.result
@@ -1456,6 +1456,68 @@ connection default;
 set old_mode= @old_old_mode;
 drop table t1;
 set debug_sync= reset;
+#
+# MDEV-32100 Online ALTER TABLE ends with 1032 under some isolation levels
+#
+create table iso_levels(id int, level text);
+INSERT iso_levels VALUES (0, "READ UNCOMMITTED"),
+(1, "READ COMMITTED"),
+(2, "REPEATABLE READ"),
+(3, "SERIALIZABLE");
+create table t1 (a int, b int, key(b)) engine=innodb;
+connection con2;
+insert into t1 values (1,1),(null,null),(3,3),(4,null),(null,5);
+connection default;
+set session transaction isolation level SERIALIZABLE;
+set debug_sync= "alter_table_online_downgraded signal downgraded wait_for goalters";
+alter table t1 force, algorithm=copy;
+connection con2;
+set debug_sync= "now wait_for downgraded";
+delete from t1 where b is null;
+set debug_sync= "now signal goalters";
+connection default;
+drop table t1;
+create table t1 (a int, b int, key(b)) engine=innodb;
+connection con2;
+insert into t1 values (1,1),(null,null),(3,3),(4,null),(null,5);
+connection default;
+set session transaction isolation level REPEATABLE READ;
+set debug_sync= "alter_table_online_downgraded signal downgraded wait_for goalters";
+alter table t1 force, algorithm=copy;
+connection con2;
+set debug_sync= "now wait_for downgraded";
+delete from t1 where b is null;
+set debug_sync= "now signal goalters";
+connection default;
+drop table t1;
+create table t1 (a int, b int, key(b)) engine=innodb;
+connection con2;
+insert into t1 values (1,1),(null,null),(3,3),(4,null),(null,5);
+connection default;
+set session transaction isolation level READ COMMITTED;
+set debug_sync= "alter_table_online_downgraded signal downgraded wait_for goalters";
+alter table t1 force, algorithm=copy;
+connection con2;
+set debug_sync= "now wait_for downgraded";
+delete from t1 where b is null;
+set debug_sync= "now signal goalters";
+connection default;
+drop table t1;
+create table t1 (a int, b int, key(b)) engine=innodb;
+connection con2;
+insert into t1 values (1,1),(null,null),(3,3),(4,null),(null,5);
+connection default;
+set session transaction isolation level READ UNCOMMITTED;
+set debug_sync= "alter_table_online_downgraded signal downgraded wait_for goalters";
+alter table t1 force, algorithm=copy;
+connection con2;
+set debug_sync= "now wait_for downgraded";
+delete from t1 where b is null;
+set debug_sync= "now signal goalters";
+connection default;
+drop table t1;
+set debug_sync= reset;
+drop table iso_levels;
 disconnect con1;
 disconnect con2;
 #
diff --git a/mysql-test/main/alter_table_online_debug.test b/mysql-test/main/alter_table_online_debug.test
index e054c0218f5..a52e95f69ed 100644
--- a/mysql-test/main/alter_table_online_debug.test
+++ b/mysql-test/main/alter_table_online_debug.test
@@ -1695,6 +1695,47 @@ set old_mode= @old_old_mode;
 drop table t1;
 set debug_sync= reset;
 
+--echo #
+--echo # MDEV-32100 Online ALTER TABLE ends with 1032 under some isolation levels
+--echo #
+
+let $tx_iso_id=4;
+
+create table iso_levels(id int, level text);
+INSERT iso_levels VALUES (0, "READ UNCOMMITTED"),
+                         (1, "READ COMMITTED"),
+                         (2, "REPEATABLE READ"),
+                         (3, "SERIALIZABLE");
+
+while($tx_iso_id) {
+dec $tx_iso_id;
+let tx_iso= `select level from iso_levels where id = $tx_iso_id`;
+
+create table t1 (a int, b int, key(b)) engine=innodb;
+
+--connection con2
+insert into t1 values (1,1),(null,null),(3,3),(4,null),(null,5);
+
+--connection default
+
+eval set session transaction isolation level $tx_iso;
+set debug_sync= "alter_table_online_downgraded signal downgraded wait_for goalters";
+
+send alter table t1 force, algorithm=copy;
+
+--connection con2
+set debug_sync= "now wait_for downgraded";
+delete from t1 where b is null;
+set debug_sync= "now signal goalters";
+
+--connection default
+--reap
+drop table t1;
+}
+set debug_sync= reset;
+drop table iso_levels;
+
+
 
 --disconnect con1
 --disconnect con2
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index 25d72cfb2fb..453237dbb65 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -65,6 +65,7 @@
 #include "rpl_rli.h"
 #include "log.h"
 #include "sql_debug.h"
+#include "scope.h"
 
 #ifdef _WIN32
 #include <io.h>
@@ -10236,6 +10237,12 @@ bool mysql_alter_table(THD *thd, const LEX_CSTRING *new_db,
     table_list->lock_type= TL_READ;
   }
 
+  enum_tx_isolation iso_level_initial= thd->tx_isolation;
+  SCOPE_EXIT([thd, iso_level_initial](){
+    thd->tx_isolation= iso_level_initial;
+  });
+  thd->tx_isolation= ISO_REPEATABLE_READ;
+
   DEBUG_SYNC(thd, "alter_table_before_open_tables");
 
   thd->open_options|= HA_OPEN_FOR_ALTER;