Assertion `!fts_index' failed in prepare_inplace_alter_table_dict

--source include/have_innodb.inc

CREATE TABLE t1 (a VARCHAR(8), b VARCHAR(8)) ENGINE=InnoDB;

ALTER TABLE t1 ADD FULLTEXT(b), ADD FULLTEXT(a);

# Cleanup

DROP TABLE t1;

mysqld: /data/src/10.3/storage/innobase/handler/handler0alter.cc:5423: bool prepare_inplace_alter_table_dict(Alter_inplace_info*, const TABLE*, const TABLE*, const char*, ulint, ulint, ulint, bool, bool): Assertion `!fts_index' failed.

171216  3:21:29 [ERROR] mysqld got signal 6 ;

#7  0x00007f21c8457ee2 in __assert_fail () from /lib/x86_64-linux-gnu/libc.so.6

#8  0x00005621228fb85f in prepare_inplace_alter_table_dict (ha_alter_info=0x7f21c0056520, altered_table=0x7f2170168e40, old_table=0x7f21700da2c0, table_name=0x7f217000e035 "t1", flags=33, flags2=94, fts_doc_id_col=2, add_fts_doc_id=true, add_fts_doc_id_idx=true) at /data/src/10.3/storage/innobase/handler/handler0alter.cc:5423

#9  0x00005621228ffba9 in ha_innobase::prepare_inplace_alter_table (this=0x7f217000c988, altered_table=0x7f2170168e40, ha_alter_info=0x7f21c0056520) at /data/src/10.3/storage/innobase/handler/handler0alter.cc:6842

#10 0x00005621225989bb in handler::ha_prepare_inplace_alter_table (this=0x7f217000c988, altered_table=0x7f2170168e40, ha_alter_info=0x7f21c0056520) at /data/src/10.3/sql/handler.cc:4231

#11 0x0000562122397b0c in mysql_inplace_alter_table (thd=0x7f2170000b00, table_list=0x7f2170014c60, table=0x7f21700da2c0, altered_table=0x7f2170168e40, ha_alter_info=0x7f21c0056520, inplace_supported=HA_ALTER_INPLACE_SHARED_LOCK_AFTER_PREPARE, target_mdl_request=0x7f21c0056590, alter_ctx=0x7f21c0057150) at /data/src/10.3/sql/sql_table.cc:7357

#12 0x000056212239d10b in mysql_alter_table (thd=0x7f2170000b00, new_db=0x7f2170015270 "test", new_name=0x0, create_info=0x7f21c0057d60, table_list=0x7f2170014c60, alter_info=0x7f21c0057cb0, order_num=0, order=0x0, ignore=false) at /data/src/10.3/sql/sql_table.cc:9395

#13 0x000056212241d5c7 in Sql_cmd_alter_table::execute (this=0x7f21700153f8, thd=0x7f2170000b00) at /data/src/10.3/sql/sql_alter.cc:331

#14 0x00005621222cda6d in mysql_execute_command (thd=0x7f2170000b00) at /data/src/10.3/sql/sql_parse.cc:6248

#15 0x00005621222d247e in mysql_parse (thd=0x7f2170000b00, rawbuf=0x7f2170014b58 "ALTER TABLE t1 ADD FULLTEXT(b), ADD FULLTEXT(a)", length=47, parser_state=0x7f21c0059610, is_com_multi=false, is_next_command=false) at /data/src/10.3/sql/sql_parse.cc:7963

#16 0x00005621222bfe11 in dispatch_command (command=COM_QUERY, thd=0x7f2170000b00, packet=0x7f2170160d01 "ALTER TABLE t1 ADD FULLTEXT(b), ADD FULLTEXT(a)", packet_length=47, is_com_multi=false, is_next_command=false) at /data/src/10.3/sql/sql_parse.cc:1825

#17 0x00005621222be845 in do_command (thd=0x7f2170000b00) at /data/src/10.3/sql/sql_parse.cc:1370

#18 0x0000562122418140 in do_handle_one_connection (connect=0x562124f230d0) at /data/src/10.3/sql/sql_connect.cc:1420

#19 0x0000562122417ecd in handle_one_connection (arg=0x562124f230d0) at /data/src/10.3/sql/sql_connect.cc:1326

#20 0x00005621228a05c6 in pfs_spawn_thread (arg=0x562124f3fce0) at /data/src/10.3/storage/perfschema/pfs.cc:1863

#21 0x00007f21ca12e494 in start_thread (arg=0x7f21c005a700) at pthread_create.c:333

#22 0x00007f21c851493f in clone () from /lib/x86_64-linux-gnu/libc.so.6