diff --git a/mysql-test/main/long_unique_innodb.result b/mysql-test/main/long_unique_innodb.result
index 8c23d61f2bc..d5694d04325 100644
--- a/mysql-test/main/long_unique_innodb.result
+++ b/mysql-test/main/long_unique_innodb.result
@@ -181,3 +181,78 @@ pk	b
 1	foo
 drop table t1;
 # End of 10.6 tests
+#
+# MDEV-35026 ALTER TABLE loses USING HASH on a unique key
+#
+create table t (
+id int(10) unsigned not null auto_increment,
+x int(10) unsigned default null,
+y int(10) unsigned default null,
+primary key (id),
+unique key y (y) using hash,
+key fk_1 (x),
+constraint fk_1 foreign key (x) references t (id)
+) engine=innodb;
+insert t select seq, seq, seq from seq_1_to_1001;
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+  `x` int(10) unsigned DEFAULT NULL,
+  `y` int(10) unsigned DEFAULT NULL,
+  PRIMARY KEY (`id`),
+  UNIQUE KEY `y` (`y`) USING HASH,
+  KEY `fk_1` (`x`),
+  CONSTRAINT `fk_1` FOREIGN KEY (`x`) REFERENCES `t` (`id`)
+) ENGINE=InnoDB AUTO_INCREMENT=1002 DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+alter table t drop foreign key fk_1;
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+  `x` int(10) unsigned DEFAULT NULL,
+  `y` int(10) unsigned DEFAULT NULL,
+  PRIMARY KEY (`id`),
+  UNIQUE KEY `y` (`y`) USING HASH,
+  KEY `fk_1` (`x`)
+) ENGINE=InnoDB AUTO_INCREMENT=1002 DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+alter table t drop column x;
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
+  `y` int(10) unsigned DEFAULT NULL,
+  PRIMARY KEY (`id`),
+  UNIQUE KEY `y` (`y`) USING HASH
+) ENGINE=InnoDB AUTO_INCREMENT=1002 DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table t;
+# Engine change must not keep the hidden hash column
+create table t (a int, unique (a) using hash) engine=innodb;
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` int(11) DEFAULT NULL,
+  UNIQUE KEY `a` (`a`) USING HASH
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+alter table t engine=memory;
+select engine from information_schema.tables where table_schema=database() and table_name='t';
+engine
+MEMORY
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` int(11) DEFAULT NULL,
+  UNIQUE KEY `a` (`a`)
+) ENGINE=MEMORY DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+alter table t engine=myisam;
+select engine from information_schema.tables where table_schema=database() and table_name='t';
+engine
+MyISAM
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` int(11) DEFAULT NULL,
+  UNIQUE KEY `a` (`a`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+drop table t;
+# End of 10.11 tests
diff --git a/mysql-test/main/long_unique_innodb.test b/mysql-test/main/long_unique_innodb.test
index fc51817e45a..dfbcc8ed30d 100644
--- a/mysql-test/main/long_unique_innodb.test
+++ b/mysql-test/main/long_unique_innodb.test
@@ -1,5 +1,6 @@
 --source include/have_innodb.inc
 --source include/have_partition.inc
+--source include/have_sequence.inc
 
 #
 # MDEV-371 Unique indexes for blobs
@@ -187,3 +188,38 @@ select * from t1;
 drop table t1;
 
 --echo # End of 10.6 tests
+
+--echo #
+--echo # MDEV-35026 ALTER TABLE loses USING HASH on a unique key
+--echo #
+
+create table t (
+  id int(10) unsigned not null auto_increment,
+  x int(10) unsigned default null,
+  y int(10) unsigned default null,
+  primary key (id),
+  unique key y (y) using hash,
+  key fk_1 (x),
+  constraint fk_1 foreign key (x) references t (id)
+) engine=innodb;
+
+insert t select seq, seq, seq from seq_1_to_1001;
+show create table t;
+alter table t drop foreign key fk_1;
+show create table t;
+alter table t drop column x;
+show create table t;
+drop table t;
+
+--echo # Engine change must not keep the hidden hash column
+create table t (a int, unique (a) using hash) engine=innodb;
+show create table t;
+alter table t engine=memory;
+select engine from information_schema.tables where table_schema=database() and table_name='t';
+show create table t;
+alter table t engine=myisam;
+select engine from information_schema.tables where table_schema=database() and table_name='t';
+show create table t;
+drop table t;
+
+--echo # End of 10.11 tests
diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index f524a52ec2a..a0452039827 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -9265,15 +9265,24 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       enum Key::Keytype key_type;
       LEX_CSTRING tmp_name;
       bzero((char*) &key_create_info, sizeof(key_create_info));
-      if (key_info->algorithm == HA_KEY_ALG_LONG_HASH)
-        key_info->algorithm= alter_ctx->fast_alter_partition ?
-          HA_KEY_ALG_HASH : HA_KEY_ALG_UNDEF;
       /*
-        For fast alter partition we set HA_KEY_ALG_HASH above to make sure it
-        doesn't lose the hash property.
-        Otherwise we let mysql_prepare_create_table() decide if the hash field
-        is needed depending on the (possibly changed) data types.
+        All columns of a long hash key survive here, so the key keeps
+        HA_KEY_ALG_LONG_HASH unless a column was changed or the storage engine
+        is changed.
+        For fast alter partition we set HA_KEY_ALG_HASH
+        to make sure it doesn't lose the hash property.
+        Otherwise we let mysql_prepare_create_table() decide
+        if the hash field is needed depending on the (possibly changed)
+        data types or engine.
       */
+      if (key_info->algorithm == HA_KEY_ALG_LONG_HASH)
+      {
+        if (alter_ctx->fast_alter_partition)
+          key_info->algorithm= HA_KEY_ALG_HASH;
+        else if ((alter_info->flags & ALTER_CHANGE_COLUMN) ||
+                 create_info->db_type != table->s->db_type())
+          key_info->algorithm= HA_KEY_ALG_UNDEF;
+      }
       key_create_info.algorithm= key_info->algorithm;
       /*
         We copy block size directly as some engines, like Area, sets this